Antivirus helps to protect your computer from viruses and other threats in two ways — by monitoring your computer for viruses and by scanning the files in your file system. These two features work together to help make sure that none of the files on your computer are harboring a secret virus, and that no new viruses are getting in.
Viruses are uninvited, usually malicious programs that arrive on your computer in various ways. Most commonly, they attach themselves to files that look legitimate. A malicious program cannot cause harm to your computer unless it runs, so the first task of a virus is to try to trick you or a program on your computer into running it. When a virus runs on your computer, it can do a variety of things that range from harmless and annoying to extremely destructive.
When Antivirus finds a potentially infected file on your computer, it first places restrictions on the file to prevent the virus from doing harm. Then, depending on the circumstances, it takes an appropriate action. Possible actions are: displaying a dialog asking you what to do with the file; automatically trying to clean the file by removing the virus; placing the file in Quarantine (A way of changing the properties of a file that might be infected, to keep it from executing or otherwise performing actions that might harm your computer.) ; or simply continuing to prevent the file from opening.
Windows Live OneCare Antivirus updates itself automatically as new viruses are discovered and new virus definition files (A file containing descriptions or templates of the patterns used by known viruses. Also called a virus signature file.) are released. You can check the status of your Antivirus at any time by looking at the Protection Plus area of the Windows Live OneCare screen.
Sometimes, when you install a new software program, you may need to turn off your Windows Live OneCare Antivirus monitoring during installation. If you do this, it's a good idea to also disconnect your connection to the Internet. Be sure you turn your Antivirus monitoring back on again when you are finished.
By default Windows Live OneCare Antivirus monitoring checks any attachments to instant messages that come to your computer via MSN Messenger. If an attachment contains a potential virus, Antivirus blocks the file and notifies you.
For other e-mail or instant messaging programs, Antivirus monitoring checks all attachments when you try to open them, and blocks the file if it contains a potential virus.
In general, you should always use caution in opening all attachments to e-mail or instant messages.