Through various means, "flags" can be turned on or off, allowing PvP combat with other people who have also turned on their flag. In EverQuest, there is no way to turn the flag off once it has been turned on. In Star Wars Galaxies, the flag may be turned off by interacting with faction specific NPCs located throughout the game or by typing an in-game command (/pvp). In World of Warcraft, flagging is selectable or can be activated by attacking certain flagged players until a cool-off period ends, though this can be exploited by griefers via corpse camping. Some games have a bounty system where players that kill or heal other players open themselves up to being killed in return. This is sometimes called the "revenge flag". Use of this 'bounty' system is not standardized among MMORPGs, and there are debates raging about how to 'police' the system to avoid abuse.
