Free Online Antivirus Scanners

If you suspect that your computer might have a virus and you can still access the web, you can use a free online antivirus scanner to identify and eliminate any viruses that have infected your computer. An online antivirus scanner will not be as fast as an antivirus utility that is installed on your computer. An installed antivirus utility can stay active at all times and scan files as you open them. But if you don't have an installed antivirus utility, or if you let your subscription expire, an online antivirus scanner may be your only choice.
To use an online antivirus scanner, you'll need Internet Explorer version 5.0 or higher installed on your computer. In fact, one way you can avoid getting a virus in the first place is to update your browser to the latest version. You should also make sure you have all the latest updates from Microsoft's Windows Update website.
Note: In my experience, Microsoft's update site doesn't work too well with a dial-up connection. They have the bandwidth is pinched off tight and it stalls frequently.
The first time you use an online antivirus scanner website you'll be required to download an ActiveX control. Make sure your browser is configured to accept ActiveX controls.
Symantec Security Response
Click on the "Check for security risks" icon, then click on the "Virus Detection" link. Symantec also provides a "Security Scan", which checks whether your computer is configured to be safe from hackers, viruses, and other attacks.
Trend Micro
This Tokyo company has been in the online antivirus scanner business longer than anyone else. Click on the "Personal" tab (unless you're an Enterprise). Under the heading "VIRUS ALERT", click on the link "Free Online Scan".
Panda Software
Panda Software is another company that's been in the antivirus business for a long time with computer installed utilities. Click on "Online virus check" or on the Panda ActiveScan icon. A new browser window will open with Panda ActiveScan.
RAV AntiVirus
This company's antivirus technology was acquired by Microsoft in 2003. Click on "Scan online" in the menu on the left side. The first time you use RAV AntiVirus you must download and install over 1MB of required files. On subsequent visits to the site, only the updated files (up to 100Kb, depending on how often you use the service) will need to be downloaded.
Bitdefender
This Bucharest, ROMANIA based company has Macromedia Flash on every page. If you use dial-up, that will probably bog down your connection enough to make this site useless. Do they think someone who is seeking antivirus scanning would want to download Macromedia Flash player? Macromedia Flash is used by bored webpage designers who have a lot of time on their hands and a lot of money to waste. Unless no other online antivirus scanner works for you, I would recommend avoiding this site until they lose the Flash.