Resident Evil 6 will allow you to invade other people's games and attempt to kill their characters.
Agent Hunt mode will let you surreptitiously control various mutant beasties. Your objective will be to take down another player's main character, and effectively ruin their day.
Players will be warned when a human-controlled enemy is on the loose, but will not be told which creature is controlled, reported Famitsu (via Andriasang).
Multiple players can attack at once, and use voice chat to strategise.
The mode will not be available from the off - presumably to give players some breathing space during their initial playthrough. Agent Hunt will only be unlocked when you complete the game. You'll then be able to replay stages with the Agent Hunt option toggled.
Eurogamer has a huge Resident Evil 6 preview due to go live later today - expect to hear much more then.