Ok a friend wanted help today when their norton security suit went crazy and died, I asked about what had been done on the computer and the guy had got a trojan that hadnt been picked up by his AV (Thanks AVG you saved my computer again ) However google supplyed no answers and norton didnt notice it, AVG noticed it but couldnt give any info on it. I got the dude to hijackthis his computer and i noticed some suspiciuos registry entries, now we think hes rid of it. All this however made me want to learn more about virii and trojans. I would like to learn if there are ways to analise what they do and how they do it. Im ok as far as a test box goes so i basically want to play about and see what i can find out about them. I mean how do AV companies work out whats a virus and how do they write signatures, basically im curious Thanks