Virus detection

I havn't been on the 'net all that long, and I,ve always taken the anti-virus software for granted, and never thought about how it actually works. What does it scan for...does it have a preset library of strings that it searches for etc? If so, is this library updateable?

I would be very interested to know, especially so, with the recent outbreak causing so much havoc.

GRAHAM

I'm not sure about this but I always assumed that the antivirus program would read exe right before you ran it and quickly check through it for known virus code.