Computer viruses and malicious computer programs

As the number of computer users increases and the exchange of data via the Internet and e-mail becomes more available, there is an increased threat of computer virus infection and data corruption or capture by malicious computer programs or malware.

In order to be aware of potential threats to your computer, it is helpful to know what the types of malicious software are and how they work. In general, malicious programs fall into one of the following three categories:

Worms use network resources for distribution. These programs were called "worms" because of their ability to "squirm" from one computer to another, using networks, e-mail traffic and other channels. Due to this ability, worms can spread extremely fast.

Worms penetrate a computer, determine IP addresses of other computers, and then send copies of themselves to these computers. Worms also utilize data contained in the address books of mail clients installed on the infected machine. They can also create work files on disks but may not utilize any resources of the infected computer except RAM resources.

Viruses infect computer programs by adding code to alter the way the infected programs work in order to gain control when the infected file is running. This simple definition helps determine that the main action a virus performs is infecting computer programs. Viruses spread somewhat slower than worms.
Trojan horses perform unauthorized actions on infected computers, i.e. depending on some conditions, they can erase information on hard drives, "freeze" the system, steal confidential information, etc. In the strict sense, Trojan Horses are not viruses (i.e. they do not infect programs or data), they are unable to sneak independently into computers and are distributed by intruders as "useful" software. Still the damage inflicted by Trojans may be far greater than losses from a regular virus attack.

Recently, worms have become the most widespread type of malware, followed by viruses and Trojans. Some malicious computer programs have typical features of two or even all three of the above categories.

Although malicious programs are distributed mainly via e-mail and the Internet, a floppy disk or a CD can also be a source of infection. Therefore, the task of comprehensive protection from potential threats now extends far beyond simple regular scans for viruses, and includes the more complex task of real-time anti-virus protection.

Henceforth in the text of this Help the term "virus" will be used to refer to viruses, Trojan Horses and worms. A particular type of malware will be mentioned only when it is required.