Computer Virus Information

What is a computer virus?
A computer virus is a program that attaches itself to or modifies another program or file. These programs are called "viruses" because they share some of the traits of biological viruses: they are small, self-replicating, and cannot exist without a host. Computer viruses have been known to corrupt programs, delete files, destroy data, and even reformat entire hard drives.Viruses cost businesses millions of dollars in lost data, loss of productivity, antivirus software, and time spent recovering from virus damage.

Types of Computer viruses
As a general rule, computer viruses fall into one of three categories: true viruses, worms, and Trojan horses. Some viruses are written to cause annoying but non-malicious problems on your computer. Others are written to intentionally destroy or delete files. Yet others are written to be unobtrusive pranks, but end up resulting in the worst disasters.

Virus: Includes boot sector viruses, file or program viruses, and macro viruses. These programs attach themselves to other programs or files on your computer or removeable media. When the host program executes (or host file is opened), the virus is activated. The virus then has the chance to replicate and wreak havoc.

Worm: A small piece of software that uses computer networks and security holes to replicate itself. A copy of the worm scans the network for another unprotected machine where it copies itself and starts replicating from there as well. Worms usually move from computer to computer by emailing themselves as attachments. A worm can go through the address book of the host computer, and e-mail itself to everyone in the address book.

Trojan horse: A Trojan horse program is a malicious program that pretends to be a benign application; a Trojan horse program purposefully does something the user does not expect. Trojans are not viruses since they do not replicate, but Trojan horse programs can be just as destructive.

How do I know if I have a virus?
You may suspect your computer system has been infected with a virus when...

	Unusual messages or graphics display on your monitor.
	Unusual sounds or music played at random times.
	A disk or volume name has been changed.
	Programs or files are suddenly missing.
	Unknown programs or files have been created.
	Some of your files or programs become corrupted or suddenly don't work properly.
	Your computer is continually crashing, freezing, or won't start at all.
	Your computer does not behave normally.