can you please give me a brief description of what happens when the antivirus software scans the disk. how does it find the virus. i searched on google but i could not find anything therefore i just want some basic understanding how the antivirus find the virus from the disk. and can you please tell me a brief description about virus signature what it means and whats it for. i will be very pleased if i can get the answer as soon as possible.

thanks.

Some results from Google

First of all take a look at: How Computer Viruses Work by Marshall Brain. And far as virus definitions. Think of those as 'profiles' or 'fingerprints' with which to identify viruses. This is why it is not advisable to have two active antivirus applications on your machine. They will often identify each others definitions as a threat. One active and one on demand is okay.