Quick Facts

Introduction to Viruses

1. What is a computer virus?
2. What kind of files can spread viruses?
3. How do viruses spread?
4. What do viruses do to computers?
5. Virus Hoaxes
   

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What kind of files can spread viruses?

Viruses can infect any type of executable code, not just the files that are commonly called 'program files'. Viruses can be spread by:

• Executable code in the boot sector of infected floppy disks
• Executable code in the system area of infected hard drives
• Word processing and spreadsheet documents that use infected macros
• Infected HTML documents that contain JavaScript or other types of executable code

Since virus code must be executed (run) to have any effect, files that the computer treats as pure data are safe. This includes graphics and sound files such as .gif, .jpg, .mp3, .wav, etc., as well as plain text in .txt files. For example, just viewing picture files won't infect your computer with a virus. The virus code has to be in a form, such as an .exe program file or a Word .doc file, that the computer will actually try to execute.