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What is a virus?

Computer viruses are bits of code that damage or erase information, files, or software programs in your computer. And just like in humans (or pets if your prefer,) they can spread. A computer can catch a virus when you download an infected file from the Internet or copy an infected file from a diskette. When a computer is infected with a virus it can immediately start to damage or destroy information, or it can wait for a particular date or event to trigger its activity.

• Strange characters suddenly appear on your screen
• Strange messages suddenly appear on your screen
• Hard drive errors
• Memory errors
• Software errors
• Corruption of files and directories

A few virus detection software manufacturers include Symantec, Dr. Solomon's Software, and McAfee. Because new viruses are created all the time, always be sure to get the latest version of your antivirus software.

What Viruses don't do

Computer viruses don't infect files on write-protected disks and don't infect documents, except in the case of Word macro viruses, which can only infect documents (and templates) written in Word 6.0 or higher. They don't infect compressed files either. However, applications within a compressed file could have been infected before they were compressed. Viruses also don't infect computer hardware, such as monitors or computer chips; they only infect software. In addition, Macintosh viruses don't infect DOS-based computer software and vice versa. For example, the infamous Michelangelo virus does not infect Macintosh applications. Again, an exception to this rule are the Word and Excel macro viruses, which infect just spreadsheets, documents and templates which can be opened by either Windows or Macintosh computers.

Finally, viruses don't necessarily let you know that they are there - even after they do something destructive.

How Viruses are Spread

Viruses spread when you launch an infected application or start up your computer from a disk that has infected system files. For example, if a program contains a virus, the virus activates when you run the program. Once a virus is in memory, it usually infects any application you run, including network applications (if you have write access to network folders or disks). Viruses behave in different ways. Some viruses stay active in memory until you turn off your computer. Other viruses stay active only as long as the infected applications is running. Turning off your computer or exiting the application removes the virus from memory, but does not remove the virus from the infected file or disk. That is, if the virus resides in a system file, the virus will activate the next time you start your computer from the infected disk. If the virus resides in an application, the virus will activate again when you run the application the next time.

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