VIRUS AND ANTIVIRUS,Viruses And Other Computer Infestations,worm,what is worm, what is trojan horse,trojan horse

Viruses And Other Computer Infestations

A computer support person needs to know how to protect computers against computer infestations (including viruses), how to recognize them, and how to get rid of them. Understanding what infestations are, how they work, and where they hide helps technicians deal with them successfully. A computer infestation is any unwanted program that is transmitted to a computer without the knowledge of the user or owner and that is designed to do varying degrees of damage to data and software.

Computer infestations do not damage PC hardware; however, when boot sector information is destroyed on a hard drive, it can appear as though the hard drive is physically damaged. What most people refer to as viruses really fall into four categories of computer infestations: viruses, Trojan horses, worms, and logic bombs. The four types of infestations differ in the way they spread, what damage they do, and how they hide. Because viruses are by far the most common of the four kinds of computer infestations, one of the most important defenses against computer infestations is antivirus software that is designed to discover and remove a virus.

Perhaps the most common way viruses are spread is through floppy disks that are used to boot a PC. However, a floppy disk does not have to be bootable to contain or spread a virus. A virus is a program that can replicate by attaching itself to other programs. The infected program must be executed for a virus to run. The virus might then simply replicate, or also do damage by immediately performing some harmful action. A virus might be programmed to perform a negative action in the future, such as on a particular date (for instance, Friday the 13th), or when some logic within the host program is activated.

A virus is different from a worm, a program that spreads copies of itself throughout a network without a host program. A worm is seldom seen except on a network, where it creates problems by overloading the network as it replicates.

Worms do damage by their presence rather than by performing a specific damaging act, as a virus does. A worm overloads memory or hard drive space by replicating repeatedly.

A Trojan horse is a third type of computer infestation that, like a worm, does not need a host program to work—rather, it substitutes itself for a legitimate program. Trojan horses cannot replicate themselves. (This last statement has some exceptions. One Trojan horse program was disguised as an automatic backup utility downloadable from the Internet. When used, it created backups and replicated itself to the backups. It was programmed to damage several systems on Friday the 13th. In this case, the Trojan horse program is also considered a virus because of its ability to replicate.)

Because Trojan horse infestations cannot replicate and require human intervention to move from one location to another, they are not as common as viruses. Sometimes problems on a PC caused by an error or software bug can look and act like viruses, even when no virus is involved. Sometimes software is altered with malicious intent. A logic bomb is dormant code added to software and is triggered by a predetermined time or event.