If your think you have contracted a computer virus, but your antivirus scanner still shows clean scans, it is possible for you to be infected! Not all anti-virus scanners can detect every virus. But I have found a site which should give you a better idea of your files if you think they may be infected.
The Site in question is VirusTotal.com, when you upload a file to the site, it will use 36 antivirus programs to scan your file to see if its infected and it will show you individual results for each virus program which was used. Here is a screen shot of just a few of the virus scanners which the site used:
Whats more, the virus libraries are updated as soon as new ones are issued by the software companies. There is however no 100% sure fire way of knowing if a file is really clean or not, but 36 anti virus programs in 1, has got to be better than just using your own virus scanner alone.