I've seen hackers in virtual person in TF2 on a Valve server. Permanent crits and a text spamming script. I've also seen infinite jumps and invulnerability in Metroid Prime Hunters, and modded weapons which crashed the game in the first Borderlands. Resident Evil 5 also has some glitches and hacks for infinite healing items and ridiculous weapons.
Wut bout you, Flood? What games and what hacks have you seen?
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[url=http://www.halowaypoint.com/en-us/players/ar%20is4%20nubs/haloreach/fileshare#!/?section=RenderedFilm&MapId=&GameMode=0&SearchDate=7&SortBy=2&view-select=Tile&tags=&startIndex=0]Yep. It was in Halo Reach.[/url]