Amesome game!
Great gameplay, well designed and definitely good fun.
The anti-virus/computer theme goes well with this game, especially with how the weapons are names (e.g. FIREwall, megaBITE). They upgrade nicely, although it can get a bit had to tell what's going on when you have high level firewall being shot out in front of you.
I've seen how some people are complaining about how dying takes away too many upgrades, but all arcade games like this need to be harsh when lives are lost, otherwise you could just blow everything out of your way and it would be no fun! Although maybe you could add a "fun mode" where you do just this (but don't use highscores).