From that second video from 1:01 on, it is apparent he is doing some kind of hacking.....Do you see how he snaps to the scout then turns so quickly that the walls glitch out? Even with my top mouse senseitivity, I have never been able to do THAT. The only thing saving this guy from being obvious is the large time in TF2, however, I still believe he is hacking. I have seen bette snipers than him that cannot pull off the kind of stuff he does. Other than hacking, he has some kind of sensetivity script, sound script that turns down everything than footsteps, gunfire and cloak sounds...I know, I have uncloaked about 100 feet behind him as a invisiwatch - saharen spy...and he still heard me. My verdict is that he is a hacker, this is intensified by the fact that he NEVER once tried to defend himself in-game.
By "still heard me" you mean he turned around, headshot killed you 1/10 of a second after you decloaked, and turned around again? If that is the case, same thing happened to me, more than once.
