What Is a Computer Virus?

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A computer virus is a malicious program or type of code designed to disrupt the way a computer functions. Viruses are written to spread from one computer to another and to self-replicate. A computer virus works by attaching itself to a legitimate document or program to activate the infected code. If activated, the virus can damage software, corrupt data, or destroy information.

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How do computer viruses attack?

Computer viruses remain dormant until their code is activated. This means viruses can lie in wait—attached to a file or document—until you run the infected program. While the virus is dormant, it can be difficult to detect. But once your computer is infected, any other devices on the same network are also vulnerable to infection.

The amount of devastation varies from virus to virus, but some of the most common things a virus can do are listed below.

  • Log keystrokes
  • Steal passwords
  • Send spam email (with infected code) to your contacts
  • Access and steal data
  • Corrupt files
  • Completely take over your computer

Some computer viruses are designed to create mischief (like turning all of your files into pictures of squid), which is irritating, but usually manageable. But other viruses target financial data or aim to destroy your hard drive.


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Rebecca Edwards
Written by
Rebecca Edwards
Rebecca is the lead safety reporter and in-house expert for SafeWise.com. She has been a journalist and blogger for over 25 years, with a focus on home and community safety for the past decade. Rebecca spends dozens of hours every month poring over crime and safety reports and spotting trends. Her expertise is sought after by publications, broadcast journalists, non-profit organizations, podcasts, and more. You can find her expert advice and analysis in places like NPR, TechCrunch, The Washington Post, The Chicago Tribune, The Miami Herald, HGTV, MSN, Reader's Digest, Real Simple, and an ever-growing library of podcast, radio and TV clips in the US and abroad.

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