I got excited when I read the description, but then I found myself playing another defense game. Cool idea for a game, but I’m not crazy about defense games. I did like how this one was sort of real-time, though. I just don’t like sitting and watching the little viruses wander towards the bottom of the screen, only indirectly being able to affect the play. Let me delete them directly, or try to hack the hacker, in addition to turrets! That would be fun!
I agree that the arrows need to be rigidly lined up with the beat of the music, if that’s the type of game you’re going for. Some more visual feedback would help as well. Also, were the arrows/letters randomly generated? I think it would be more fun, and add to the ‘combo’ nature, if there were patterns of arrows that people could get used to, like combos in Street Fighter. If the timing is fixed and the patterns made more sense I think it could be a fun game with a little polish.
 "Master of Security"){kind=icon}
 "Combo King"){kind=icon}