Eh, right...
Uhm... well... First of all, what bothered me most was the grammar and the spelling. That really, really annoyed me. There were just so many mistakes it more or less ruined some of the scenes. And the expression " Piece of Piss " is incorrect. It's supposed to be piece of shit, sorry to say so. The prologue was simply too long, and it seemed too easy, that he just stumbled into a guy that had stolen a military virus. You simply don't make that kind of trades on the street. And the zombie they ran into in the building... Well, I thought the rain was supposed to make them zombies? Why did this fellar lie inside then?
Sorry, I'm just kind of a grammar and spelling freak, and if things aren't done right, it just galls me. The characters were quite well done though. Their movements were stiff, but since it's your first flash, it's not so bad.