HaCKeRz Kr0nlcKLeZ 1/HaCKeRz Kr0nlcKLeZ.iso/chibacity/comp.faq/text0001.txt

Text File | 1996-04-22 | 26.7 KB | 562 lines

The use of the password command (e.g. PASSWORD/W:MINE *.EXE *.COM)
will stop more viruses than the plain DOS attribute facility, but that
isn't saying much!  The combination of the password system plus a disk
compression system may be more secure (because to bypass the password
system they must access the disk directly, but under SuperStore or
Stacker the physical disk is meaningless to the virus). There may be
some viruses which, rather than invisibly infecting files on
compressed disks in fact very visibly corrupt the disk.

The "secure disk partitions" system introduced with DR DOS 6 may be of
some help against a few viruses that look for DOS partitions on a
disk.  The main use is in stopping people fiddling with (and
infecting) your hard disk while you are away.

Furthermore, DR DOS is not very compatible with MS/PC-DOS, especially
down to the low-level tricks that some viruses are using.  For
instance, some internal memory structures are "read-only" in the sense
that they are constantly updated (for DOS compatibility) but not
really used by DR DOS, so that even if a sophisticated virus modifies
them, this does not have any effect.

In general, using a less compatible system diminishes the number of
viruses that can infect it.  For instance, the introduction of hard
disks made the Brain virus almost disappear; the introduction of 80286
and DOS 4.x+ made the Yale and Ping Pong viruses extinct, and so on.


D8) Will a write-protect tab on a floppy disk stop viruses?

In general, yes.  The write-protection on IBM PC (and compatible) and
Macintosh floppy disk drives is implemented in hardware, not software,
so viruses cannot infect a diskette when the write-protection mechanism
is functioning properly.

But remember:

(a) A computer may have a faulty write-protect system (this happens!)
    - you can test it by trying to copy a file to the diskette when it
    is presumably write-protected.
(b) Someone may have removed the tab for a while, allowing a virus on.
(c) The files may have been infected before the disk was protected.
    Even some diskettes "straight from the factory" have been known to be
    infected in the production processes.

So it is worthwhile scanning even write-protected disks for viruses.


D9) Do local area networks (LANs) help to stop viruses or do they
    facilitate their spread?

Both.  A set of computers connected in a well managed LAN, with
carefully established security settings, with minimal privileges for
each user, and without a transitive path of information flow between
the users (i.e., the objects writable by any of the users are not
readable by any of the others) is more virus-resistant than the same
set of computers if they are not interconnected.  The reason is that
when all computers have (read-only) access to a common pool of
executable programs, there is usually less need for diskette swapping
and software exchange between them, and therefore less ways through
which a virus could spread.

However, if the LAN is not well managed, with lax security, it could
help a virus to spread like wildfire.  It might even be impossible to
remove the infection without shutting down the entire LAN.

A network that supports login scripting is inherently more resistant
to viruses than one that does not, if this is used to validate the
client before allowing access to the network.


D10) What is the proper way to make backups?

Data and text files, and programs in source form, should be backed up
each time they are modified.  However, the only backups you should
keep of COM, EXE and other *executable* files are the *original*
versions, since if you back up an executable file on your hard disk
over and over, it may have become infected meanwhile, so that you may
no longer have an uninfected backup of that file.  Therefore:
  1. If you've downloaded shareware, copy it (preferably as a ZIP or
other original archive file) onto your backup medium and do not
re-back it up later.
  2. If you have purchased commercial software, it's best to create a
ZIP (or other) archive from the original diskettes (assuming they're
not copy protected) and transfer the archive onto that medium.  Again,
do not re-back up.
  3. If you write your own programs, back up only the latest version
of the *source* programs.  Depend on recompilation to reproduce the
executables.
  4. If an executable has been replaced by a new version, then of
course you will want to keep a backup of the new version.  However, if
it has been modified as a result of your having changed configuration
information, it seems safer *not* to back up the modified file; you
can always re-configure the backup copy later if you have to.
  5. Theoretically, source programs could be infected, but until such
a virus is discovered, it seems preferable to treat such files as
non-executables and back them up whenever you modify them.  The same
advice is probably appropriate for batch files as well, despite the
fact that a few batch file infectors have been discovered.


=======================================================
= Section E.    Facts and Fibs about computer viruses =
=======================================================

E1) Can boot sector viruses infect non-bootable floppy disks?

Any diskette that has been properly formatted contains an executable
program in the boot sector.  If the diskette is not "bootable," all
that boot sector does is print a message like "Non-system disk or disk
error; replace and strike any key when ready", but it's still
executable and still vulnerable to infection.  If you accidentally
turn your machine on with a "non-bootable" diskette in the drive, and
see that message, it means that any boot virus that may have been on
that diskette *has* run, and has had the chance to infect your hard
drive, or whatever.  So when thinking about viruses, the word
"bootable" (or "non-bootable") is really misleading.  All formatted
diskettes are capable of carrying a virus.


E2) Can a virus hide in a PC's CMOS memory?

No.  The CMOS RAM in which system information is stored and backed up
by batteries is ported, not addressable.  That is, in order to get
anything out, you use I/O instructions.  So anything stored there is
not directly sitting in memory.  Nothing in a normal machine loads the
data from there and executes it, so a virus that "hid" in the CMOS RAM
would still have to infect an executable object of some kind in order
to load and execute whatever it had written to CMOS.  A malicious
virus can of course *alter* values in the CMOS as part of its payload,
but it can't spread through, or hide itself in, the CMOS.

A virus could also use the CMOS RAM to hide a small part of its
body (e.g., the payload, counters, etc.).  However, any executable
code stored there must be first extracted to ordinary memory in order
to be executed.


E3) Can a virus hide in Extended or in Expanded RAM?

Theoretically yes, although no such viruses are known yet.  However,
even if they are created, they will have to have a small part resident
in conventional RAM; they cannot reside *entirely* in Extended or in
Expanded RAM.


E4) Can a virus hide in Upper Memory or in High Memory?

Yes, it is possible to construct a virus which will locate itself
in Upper Memory (640K to 1024K) or in High Memory (1024K to 1088K),
and a few currently known viruses (e.g. EDV) do hide in Upper Memory.

It might be thought that there is no point in scanning in these areas
for any viruses other than those which are specifically known to
inhabit them.  However, there are cases when even ordinary viruses can
be found in Upper Memory.  Suppose that a conventional memory-resident
virus infects a TSR program and this program is loaded high by the
user (for instance, from AUTOEXEC.BAT).  Then the virus code will also
reside in Upper Memory.  Therefore, an effective scanner must be able
to scan this part of memory for viruses too.


E5) Can a virus infect data files?

Some viruses (e.g., Frodo, Cinderella) modify non-executable files.
However, in order to spread, the virus must be executed.  Therefore
the "infected" non-executable files cannot be sources of further
infection.

However, note that it is not always possible to make a sharp
distinction between executable and non-executable files.  One man's
code is another man's data and vice versa.  Some files that are not
directly executable contain code or data which can under some
conditions be executed or interpreted.

Some examples from the IBM PC world are .OBJ files, libraries, device
drivers, source files for any compiler or interpreter, macro files
for some packages like MS Word and Lotus 1-2-3, and many others.
Currently there are viruses that infect boot sectors, master boot
records, COM files, EXE files, BAT files, and device drivers, although
any of the objects mentioned above can theoretically be used as an
infection carrier.  PostScript files can also be used to carry a virus,
although no currently known virus does that.


E6) Can viruses spread from one type of computer to another?

The simple answer is that no currently known viruses can do this.
Although the disk formats may be the same (e.g. Atari ST and DOS), the
different machines interpret the code differently.  For example, the
Stoned virus cannot infect an Atari ST as the ST cannot execute the
virus code in the bootsector.  The Stoned virus contains instructions
for the 80x86 family of CPU's that the 680x0-family CPU (Atari ST)
can't understand or execute.

The more general answer is that such viruses are possible, but
unlikely.  Such a virus would be quite a bit larger than current
viruses and might well be easier to find.  Additionally, the low
incidence of cross-machine sharing of software means that any such
virus would be unlikely to spread -- it would be a poor environment
for virus growth.


E7) Can DOS viruses run on non-DOS machines (e.g. Mac, Amiga)?

In general, no.  However, on machines running DOS emulators (either
hardware or software based), DOS viruses - just like any DOS program -
may function.  These viruses would be subject to the file access
controls of the host operating system.  An example is when running a
DOS emulator such as VP/ix under a 386 UNIX environment, DOS
programs are not permitted access to files which the host UNIX system
does not allow them to.  Thus, it is important to administer these
systems carefully.


E8) Can mainframe computers be susceptible to computer viruses?

Yes.  Numerous experiments have shown that computer viruses spread
very quickly and effectively on mainframe systems.  However, to our
knowledge, no non-research computer virus has been seen on mainframe
systems.  (The Internet worm of November 1988 was not a computer virus
by most definitions, although it had some virus-like characteristics.)

Computer viruses are actually a special case of something else called
"malicious logic", and other forms of malicious logic -- notably
Trojan horses -- are far quicker, more effective, and harder to detect
than computer viruses.  Nevertheless, on personal computers many more
viruses are written than Trojans.  There are two reasons for this:
(1) Since a virus propagates, the number of users to which damage can
be caused is much greater than in the case of a Trojan; (2) It's
almost impossible to trace the source of a virus since viruses are
not attached to any particular program.

For further information on malicious programs on multi-user systems,
see Matt Bishop's paper, "An Overview of Malicious Logic in a Research
Environment", available by anonymous FTP on Dartmouth.edu
(129.170.16.4) as "pub/security/mallogic.ps".


E9) Some people say that disinfecting files is a bad idea.  Is that
    true?

Disinfecting a file is completely "safe" only if the disinfecting
process restores the non-infected state of the object completely.  That
is, not only the virus must be removed from the file, but the original
length of the file must be restored exactly, as well as its time and
date of last modification, all fields in the header, etc.  Sometimes
it is necessary to be sure that the file is placed on the same
clusters of the disk that it occupied prior to infection.  If this is
not done, then a program which uses some kind of self-checking or
copy protection may stop functioning properly, if at all.

None of the currently available disinfecting programs do all this.
For instance, because of the bugs that exist in many viruses, some of
the information of the original file is destroyed and cannot be
recovered. Other times, it is even impossible to detect that this
information has been destroyed and to warn the user.  Furthermore,
some viruses corrupt information very slightly and in a random way
(Nomenklatura, Phoenix), so that it is not even possible to tell which
files have been corrupted.

Therefore, it is usually better to replace the infected objects with
clean backups, provided you are certain that your backups are
uninfected (see D10).  You should try to disinfect files only if they
contain some valuable data that cannot be restored from backups or
compiled from their original source.


E10) Can I avoid viruses by avoiding shareware/free software/games?

No.  There are many documented instances in which even commercial
"shrink wrap" software was inadvertently distributed containing
viruses.  Avoiding shareware, freeware, games, etc. only isolates you
from a vast collection of software (some of it very good, some of it
very bad, most of it somewhere in between...).

The important thing is not to avoid a certain type of software, but to
be cautious of ANY AND ALL newly acquired software.  Simply scanning
all new software media for known viruses would be rather effective at
preventing virus infections, especially when combined with some other
prevention/detection strategy such as integrity management of
programs.


E11) Can I contract a virus on my PC by performing a "DIR" of an
     infected floppy disk?

If you assume that the PC you are using is virus free before you
perform the DIR command, then the answer is no.  However, when you
perform a DIR, the contents of the boot sector of the diskette are
loaded into a buffer for use when determining disk layout etc., and
certain anti-virus products will scan these buffers.  If a boot sector
virus has infected your diskette, the virus code will be contained in
the buffer, which may cause some anti-virus packages to give the
message "xyz virus found in memory, shut down computer immediately".
In fact, the virus is not a threat at this point since control of the
CPU is never passed to the virus code residing in the buffer.  But,
even though the virus is really not a threat at this point, this
message should not be ignored.  If you get a message like this, and
then reboot from a clean DOS diskette and scan your hard-drive and
find no virus, then you know that the false positive was caused by the
fact that the infected boot-sector was loaded into a buffer, and the
diskette should be appropriately disinfected before use.  The use of
DIR will not infect a clean system, even if the diskette it is being
performed on does contain a virus.


E12) Is there any risk in copying data files from an infected floppy
    disk to a clean PC's hard disk?

Assuming that you did not boot or run any executable programs from the
infected disk, the answer is generally no.  There are two caveats: 1)
you should be somewhat concerned about checking the integrity of these
data files as they may have been destroyed or altered by the virus,
and 2) if any of the "data" files are interpretable as executable by
some other program (such as a Lotus macro) then these files should be
treated as potentially malicious until the symptoms of the infection
are known.  The copying process itself is safe (given the above
scenario).  However, you should be concerned with what type of files
are being copied to avoid introducing other problems.


E13) Can a DOS virus survive and spread on an OS/2 system using the
     HPFS file system?

Yes, both file-infecting and boot sector viruses can infect HPFS
partitions.  File-infecting viruses function normally and can activate
and do their dirty deeds, and boot sector viruses can prevent OS/2
from booting if the primary bootable partition is infected.  Viruses
that try to directly address disk sectors cannot function because OS/2
prevents this activity.


E14) Under OS/2 2.0, could a virus infected DOS session infect another
    DOS session?

Each DOS program is run in a separate Virtual DOS Machine (their
memory spaces are kept separated by OS/2).  However, any DOS program
has almost complete access to the files and disks, so infection can
occur if the virus infects files; any other DOS session that executes
a program infected by a virus that makes itself memory resident would
itself become infected.

However, bear in mind that all DOS sessions share the same copy of the
command interpreter.  Hence if it becomes infected, the virus will be
active in *all* DOS sessions.


E15) Can normal DOS viruses work under MS Windows?

Most of them cannot.  A system that runs exclusively MS Windows is,
in general, more virus-resistant than a plain DOS system.  The reason
is that most resident viruses are not compatible with the memory
management in Windows.  Furthermore, most of the existing viruses will
damage the Windows applications if they try to infect them as normal
EXE files.  The damaged applications will stop working and this will
alert the user that something is wrong.

However, virus-resistant is by no means virus-proof.  For instance,
most of the well-behaved resident viruses that infect only COM files
(Cascade is an excellent example), will work perfectly in a DOS
window.  All non-resident COM infectors will be able to run and infect
too.  And currently there exists at least one Windows-specific virus
which is able to properly infect Windows applications (it is
compatible with the NewEXE file format).

Any low level trapping of Interrupt 13, as by resident boot sector and
MBR viruses, can also affect Windows operation, particularly if
protected disk access (32BitDiskAccess=ON in SYSTEM.INI) is used.


=========================================
= Section F.    Miscellaneous Questions =
=========================================

F1) How many viruses are there?

It is not possible to give an exact number because new viruses are
being created literally every day.  Furthermore, different anti-virus
researchers use different criteria to decide whether two viruses are
different or one and the same.  Some count viruses as different if
they differ by at least one bit in their non-variable code.  Others
group the viruses in families and do not count the closely related
variants in one family as different viruses.

Taking a rough average, as of October 1992 there were about 1,800 IBM
PC viruses, about 150 Amiga viruses, about 30 Macintosh viruses, about
a dozen Acorn Archimedes viruses, several Atari ST viruses, and a few
Apple II viruses.

However, very few of the existing viruses are widespread.  For
instance, only about three dozen of the known IBM PC viruses are
causing most of the reported infections.


F2) How do viruses spread so quickly?

This is a very complex issue.  Most viruses don't spread very quickly.
Those that do spread widely are able to do so for a variety of
reasons.  A large target population (i.e., millions of compatible
computers) helps...  A large virus population helps...  Vendors whose
quality assurance mechanisms rely on, for example, outdated scanners
help...  Users who gratuitously insert new software into their systems
without making any attempt to test for viruses help...  All of these
things are factors.


F3) What is the plural of "virus"?  "Viruses" or "viri" or "virii" or...

The correct English plural of "virus" is "viruses."  The Latin word is
a mass noun (like "air"), and there is no correct Latin plural.
Please use "viruses," and if people use other forms, please don't use
VIRUS-L/comp.virus to correct them.


F4) When reporting a virus infection (and looking for assistance), what
    information should be included?

People frequently post messages to VIRUS-L/comp.virus requesting
assistance on a suspected virus problem.  Quite often, the information
supplied is not sufficient for the various experts on the list to be
able to help out.  Also note that any such assistance from members of
the list is provided on a volunteer basis; be grateful for any help
received.  Try to provide the following information in your requests
for assistance:
        - The name of the virus (if known);
        - The name of the program that detected it;
        - The version of the program that detected it;
        - Any other anti-virus software that you are running and
whether it has been able to detect the virus or not, and if yes, by
what name did it call it;
        - Your software and hardware configuration (computer type,
kinds of disk(ette) drives, amount of memory and configuration
(extended/expanded/conventional), TSR programs and device drivers
used, OS version, etc.)

It is helpful if you can use more than one scanning program to
identify a virus, and to say which scanner gave which identification.
However, some scanning programs leave "signatures" in memory which
will confuse others, so it is best to do a "cold reboot" between runs
of successive scanners, particularly if you are getting confusing
results.


F5) How often should we upgrade our anti-virus tools to minimize
    software and labor costs and maximize our protection?

This is a difficult question to answer.  Antiviral software is a kind
of insurance, and these type of calculations are difficult.

There are two things to watch out for here: the general "style" of the
software, and the signatures which scanners use to identify viruses.
Scanners should be updated more frequently than other software, and it
is probably a good idea to update your set of signatures at least once
every two months.

Some antiviral software looks for changes to programs or specific
types of viral "activity," and these programs generally claim to be
good for "all current and future viral programs."  However, even these
programs cannot guarantee to protect against all future viruses, and
should probably be upgraded once per year.

Of course, not every anti-virus product is effective against all
viruses, even if upgraded regularly.  Thus, do *not* depend on the
fact that you have upgraded your product recently as a guarantee that
your system is free of viruses!


=====================================================================
= Section G.    Specific Virus and Anti-viral software Questions... =
=====================================================================


G1) I was infected by the Jerusalem virus and disinfected the infected
    files with my favorite anti-virus program.  However, Wordperfect
    and some other programs still refuse to work.  Why?

The Jerusalem virus and WordPerfect 4.2 program combination is an
example of a virus and program that cannot be completely disinfected
by an anti-virus tool.  In some cases such as this one, the virus will
destroy code by overwriting it instead of appending itself to the
file.  The only solution is to re-install the programs from clean
(non-infected) backups or distribution media.  (See question D10.)


G2) I was told that the Stoned virus displays the text "Your PC is now
    Stoned" at boot time.  I have been infected by this virus several
    times, but have never seen the message.  Why?

The "original" Stoned message was ".Your PC is now Stoned!", where the
"." represents the "bell" character (ASCII 7 or "PC speaker beep").
The message is displayed with a probability of 1 in 8 only when a PC is
booted from an infected diskette.  When booting from an infected hard
disk, Stoned never displays this message.

Recently, versions of Stoned with no message whatsoever or only the
leading bell character have become very common.  These versions of
Stoned are likely to go unnoticed by all but the most observant, even
when regularly booting from infected diskettes.

Contrary to some reports, the Stoned virus -does NOT- display the
message "LEGALISE MARIJUANA", although such a string is quite clearly
visible in the boot sectors of diskettes infected with the "original"
version of Stoned in "standard" PC's.


G3) I was infected by both Stoned and Michelangelo.  Why has my
    computer became unbootable?  And why, each time I run my favorite
    scanner, does it find one of the viruses and say that it is
    removed, but when I run it again, it says that the virus is still
    there?

These two viruses store the original Master Boot Record at one and the
same place on the hard disk.  They do not recognize each other, and
therefore a computer can become infected with both of them at the same
time.

The first of these viruses that infects the computer will overwrite
the Master Boot Record with its body and store the original MBR at a
certain place on the disk.  So far, this is normal for a boot-record
virus.  But if now the other virus infects the computer too, it will
replace the MBR (which now contains the virus that has come first)
with its own body, and store what it believes is the original MBR (but
in fact is the body of the first virus) AT THE SAME PLACE on the hard
disk, thus OVERWRITING the original MBR.  When this happens, the
contents of the original MBR are lost.  Therefore the disk becomes
non-bootable.

When a virus removal program inspects such a hard disk, it will see
the SECOND virus in the MBR and will try to remove it by overwriting
it with the contents of the sector where this virus normally stores
the original MBR.  However, now this sector contains the body of the
FIRST virus.  Therefore, the virus removal program will install the
first virus in trying to remove the second.  In all probability it
will not wipe out the sector where the (infected) MBR has been stored.

When the program is run again, it will find the FIRST virus in the
MBR.  By trying to remove it, the program will get the contents of the
sector where this virus normally stores the original MBR, and will
move it over the current (infected) MBR.  Unfortunately, this sector
still contains the body of the FIRST virus.  Therefore, the body of
this virus will be re-installed over the MBR ad infinitum.

There is no easy solution to this problem, since the contents of the
original MBR is lost.  The only solution for the anti-virus program is
to detect that there is a problem, and to overwrite the contents of
the MBR with a valid MBR program, which the anti-virus program will
have to carry with itself.  If your favorite anti-virus program is not
that smart, consider replacing it with a better one, or just boot from
a write-protected uninfected DOS 5.0 diskette, and execute the program
FDISK with the option /MBR.  This will re-create the executable code
in the MBR without modifying the partition table data.

In general, infection by multiple viruses of the same file or area is
possible and vital areas of the original may be lost.  This can make
it difficult or impossible for virus disinfection tools to be
effective, and replacement of the lost file/area will be necessary.

====================
[End of VIRUS-L/comp.virus FAQ]