How do antivirus programs work?
Antivirus programs work in two ways. First, they examine files for matches to the virus definition of known viruses. Because new kinds of viruses are created all the time, a good antivirus program constantly updates your virus definition files.
Second, many antivirus programs track what the files on your computer try to do. If a file tries to do something unusual for its file type, a good antivirus program detects that behavior and blocks the file. An example of a file that behaves unusually is a picture file that tries to create a connection to the Internet. By detecting this kind of behavior, an antivirus program can catch new viruses even before they are identified.
Windows Live OneCare Antivirus programs use both methods of protection to help keep your computer free of viruses. Whenever you use your computer, Antivirus automatically checks any file your computer touches, whether it’s part of a web page you’re browsing, part of an instant message, or accessed by a program. During regular Tune-ups, Antivirus also checks your computer to help make sure that no viruses are present.
If a potential virus is found, Antivirus immediately prevents the file from opening or performing any actions that might harm your computer. If a virus is found when a file opens, Antivirus displays a dialog box that asks if you want Antivirus to try to clean the file for you. If the file can't be cleaned, a dialog box asks you if you want to delete it. If a virus is found during a scan, Antivirus automatically takes appropriate steps to help correct the problem.
To help make sure that your computer is protected against the latest threats, Windows Live OneCare automatically updates your virus definition files with the Windows Live OneCare update service.
A pop-up window appears over or under your browser's main window when you visit some websites. Because a pop-up window is not a virus, Windows Live OneCare Antivirus will not remove or disable it.
Learn more on the Web
Microsoft Security Antivirus Information page