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Malware: Viruses, Spyware, Adware & Other Malicious Software

This page provides an overview of the most common malware applications. For specific steps you can take to protect against malware, see our Protect Against Viruses & Security Threats pages.

What is Malware?

Malware is a catch-all term for various malicious software, including viruses, adware, spyware, browser hijacking software, and fake security software.

Once installed on your computer, these programs can seriously affect your privacy and your computer's security. For example, malware is known for relaying personal information to advertisers and other third parties without user consent. Some programs are also known for containing worms and viruses that cause a great deal of computer damage.

Types of Malware

  • Viruses which are the most commonly-known form of malware and potentially the most destructive. They can do anything from erasing the data on your computer to hijacking your computer to attack other systems, send spam, or host and share illegal content.
  • Spyware collects your personal information and passes it on to interested third parties without your knowledge or consent. Spyware is also known for installing Trojan viruses.
  • Adware displays pop-up advertisements when you are online.
  • Fake security software poses as legitimate software to trick you into opening your system to further infection, providing personal information, or paying for unnecessary or even damaging "clean ups".
  • Browser hijacking software changes your browser settings (such as your home page and toolbars), displays pop-up ads and creates new desktop shortcuts. It can also relay your personal preferences to interested third parties.

Facts about Malware

Malware is often bundled with other software and may be installed without your knowledge.
For instance, AOL Instant Messenger comes with WildTangent, a documented malware program. Some peer-to-peer (P2P) applications, such as KaZaA, Gnutella, and LimeWire also bundle spyware and adware. While End User License Agreements (EULA) usually include information about additional programs, some malware is automatically installed, without notification or user consent.

Malware is very difficult to remove.
Malware programs can seldom be uninstalled by conventional means. In addition, they ‘hide’ in unexpected places on your computer (e.g., hidden folders or system files), making their removal complicated and time-consuming. In some cases, you may have to reinstall your operating system to get rid of the infection completely.

Malware threatens your privacy.
Malware programs are known for gathering personal information and relaying it to advertisers and other third parties. The information most typically collected includes your browsing and shopping habits, your computer's IP address, or your identification information.

Malware threatens your computer’s security.
Some types of malware contain files commonly identified as Trojan viruses. Others leave your computer vulnerable to viruses. Regardless of type, malware is notorious for being at the root, whether directly or indirectly, of virus infection, causing conflicts with legitimate software and compromising the security of any operating system, Windows or Macintosh.

How do I know if I have Malware on my computer?

Common symptoms include:

Browser crashes & instabilities

  • Browser closes unexpectedly or stops responding.
  • The home page changes to a different website and cannot be reset.
  • New toolbars are added to the browser.
  • Clicking a link does not work or you are redirected to an unrelated website.

Poor system performance

  • Internet connection stops unexpectedly.
  • Computer stops responding or takes longer to start.
  • Applications do not open or are blocked from downloading updates (especially security programs).
  • New icons are added to desktop or suspicious programs are installed.
  • Certain system settings or configuration options become unavailable.


  • Ads pop up even when the browser is not open.
  • Browser opens automatically to display ads.
  • New pages open in browser to display ads.
  • Search results pages display only ads.