After you open and run an infected program or attachment on your computer, you might not realize that you've introduced a virus until you notice something isn't quite right.

Here are a few primary indicators that your computer might be infected:

Your computer runs more slowly than normal
Your computer stops responding or locks up often
Your computer crashes and restarts every few minutes
Your computer restarts on its own and then fails to run normally
Applications on your computer don't work correctly
Disks or disk drives are inaccessible
You can't print correctly
You see unusual error messages
You see distorted menus and dialog boxes

These are common signs of infection—but they might also indicate hardware or software problems that have nothing to do with a virus. Unless you run the Microsoft Malicious Software Removal Tool and install industry-standard, up-to-date antivirus software on your computer, there is no way to be certain if your computer is infected with a virus or not. If you don't have current antivirus software installed or if you're interested in installing a different brand, visit our Windows Marketplace for software from other companies.

Tip: Beware of messages warning you that you sent e-mail that contained a virus. This can indicate that the virus has listed your e-mail address as the sender of tainted e-mail. This does not necessarily mean you have a virus. Some viruses have the ability to forge e-mail addresses.