What is a virus?

Computer viruses are self-reproducing malicious software that wreak havoc on devices and spread from one file to another, then one device to another, frequently via email attachments, drive-by-downloads, and USB drives. Viruses need human action to spread.

What they are after

Most viruses attach themselves to executable files, but on occasion, they also affect MS Office macros, auto-run scripts, and the master boot record. Viruses are largely disruptive in nature: they display irritating messages, disrupt the functioning of a device, corrupt files, or delete them altogether. In certain cases, viruses can also steal information.

Known cases

  • The Concept Virus that was accidentally shipped on a CD-ROM by Microsoft in 1995.
  • Chernobyl virus used to strike every year on April 26, marking the anniversary of the Chernobyl nuclear accident.
  • The Melissa virus, which spread via email and allegedly caused $80 million in damage.

How to block viruses

Avira Free Antivirus protects you from viruses.

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The Avira Security Wordbook

Search our threat glossary for clarifications on frequently used terms in IT security.