I remember playing around with MoSucker (Trojan).
When I first started, I remember creating the "server" (the infected file), and then trying to open it but nothing would happen... I now obviously know that I was infecting MYSELF haha.
Once I got the hang of it, I was messing with all my MSN buddies. No damage caused, just general fun.

That must of been about 12 years ago now. wow.