Software used to infect a computer. After the virus code is written, it is buried within an existing program. Once that program is executed, the virus code is activated and attaches copies of itself to other programs in the system. Infected programs copy the virus to other programs.|
The effect of the virus may be a simple prank that pops up a message on screen out of the blue, or it may destroy programs and data right away or on a certain date. It can lay dormant and do its damage once a year. For example, the Michelangelo virus contaminates the machine on Michelangelo's birthday.
Viruses Must Be Run to Do Damage
A virus is not inserted into data. It is a self-contained program or code that attaches itself to an existing application in a manner that causes it to be executed when the application is run. Macro viruses, although hidden within documents (data), are similar. It is in the execution of the macro that the damage is done.
E-Mail Attachments Are Suspect
Files attached to e-mail messages are a common way of infecting a computer when the recipient is not aware of file types that are potentially harmful. For example, files with extensions such as .EXE, .BAT and .COM can perform any operation within the computer and should never be clicked unless the user is expecting the attachment. See dangerous extensions and double extension.
Viruses Are Relatively Recent
The term virus was coined in the early 1980s, supposedly after a graduate student presented the concept of a program that could "infect" other programs. Since then, more than 80,000 viruses have been defined. However, 99% of the infections are from only a few hundred variants found "in the wild."
Since 1993, the WildList Organization has been keeping track of virus attacks around the world. For more information, visit www.wildlist.org. For a sampling of different virus infections, see virus examples. See in the wild, quarantine, disinfect, macro virus, e-mail virus, behavior blocking, polymorphic virus, stealth virus, worm, boot virus, vandal, virus hoaxes and crypto rage.
Be Careful Out There!
If you use the Internet for any purpose, be sure you have an antivirus program running at all times (see antivirus program).