The POH Glitch is a newly discovered glitch that is also used as a scam. It involves a player having a POH dungeon and attacking the player at low health. When the player is about to receive the final blow the host will expel all guests, leaving the victim taking the damage outside and losing all but 3 items. The owner of the house will usually use a super poisoned dragon dagger to poison the victims so that they die fairly quickly outside the house. This has been addressed on the forums and rants because players have lost millions due to this glitch.
If you see a high level player inviting you to to his/her dungeon for a fight or party, do NOT bring any your expensive items if you're not willing to lose them in the dungeon, and be careful if you don't trust the host.
JaGeX has fixed this glitch, and it can no longer happen. You should be aware though. They may find another way to kill high leveled players.