In case you are really paranoid – or just want to compare the ability for various anti-virus products to detect viruses, a new service may be of interest to you.
VirusTotal lets you upload a file, which they scan with 32 different anti-virus products. They tell you which (if any) anti-virus products detected malware in the file you upload.
Peter H. Gregory 
There are other similar services of free antivirus online:
– Jotti – 19 antivirus
– VirScan – 36 antivirus
– e-Antivirus – 12 antivirus
– NoVirusThanks – 21 antivirus
– FilterBit – 10 antivirus
A greeting.