Computer viruses and malicious computer programs

As the number of computer users increases and the exchange of data via the Internet and email 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 ("malware") 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 tunnel from one computer to another, using networks, email and other channels. Due to this ability, worms can spread extremely fast.

Worms penetrate a computer, determine IP addresses of other computers, and 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 create work files on disks but may not utilize any resources of the infected computer except memory.

Viruses infect computer programs by altering the way that infected programs work to gain control when the infected program 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: for instance, they can erase information on hard drives, "freeze" the system, steal confidential information. In the strict sense, Trojan Horses are not viruses as they do not infect programs or data, and are unable to sneak independently into computers but are distributed by malicious users as "useful" software. Still the damage inflicted by Trojans may be far greater than 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 characteristics of two or even all three of the above categories.

Although malicious programs are distributed mainly via email 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.