Virus is one of the most annoying thing when infects the computers, sometimes the virus activity was not seen, but it was secretly using the computer resources or bandwidth. To find out if your computer is infected or not, of course you have to scan the entire contents of your hard disk.
All antivirus software has the ability to scan, but to obtain better results, I suggest you to use the online virus scanner. Because the viruses database is always well updated and it can reduce the use of computer resources. You can find many online virus scanners, I suggest the following three online virus scanners.
This is the fastest online virus scanner, they also provide Firefox add-on, Chrome Extension, iGoogle Gadget, and website widget.
Panda ActiveScan must be run in Internet Explorer (IE). 
ESET Online Scanner also need the Internet Explorer, but if you don’t want to use IE, you can download the ESET Smart Installer.
