Virus Basics

Types:

• Virus: A program that infects files but relies on humans to be copied from computer to computer. Viruses are either malignant (cause data damage or loss) or benign (cause little or no damage).
  

• Trojan horse: A program that contains a virus "payload", which infects the computer when the program is run.  Trojan horses cannot reproduce and must rely on humans to spread the infection.
  

• Worm: A program that attempts to spread itself from computer to computer, usually without human help.

Myths:

While viruses are capable of damaging systems, they cannot do the following: (from Symantec Corp; http://www.symantec.com )

• Viruses don't infect files on write-protected disks.

• Viruses don't infect compressed files. However, applications within a compressed file could have been infected before they were compressed. Some viruses are known to insert copies of themselves in already-created archives.
  

• Viruses don't infect computer hardware such as monitors or computer chips; they only infect software. They can, however, damage certain types of hardware such as flash-memory.
  

• Macintosh viruses don't infect DOS-based computer software, and vice versa. For example, the Michelangelo virus does not infect Macintosh applications. Again, an exception to this rule are the Word and Excel macro viruses, which infect spreadsheets, documents, and templates which can be opened by either Windows or Macintosh computers.
  

• Viruses usually do not identify themselves as viruses, even after they do something destructive.