They travel in groups of up to 20, and do not attack the player unless the player attacks them first. Zombie Pigmen are able to drown, but cannot be killed by lava. Because they are well-armed, Zombie Pigmen are highly dangerous to an unsuspecting player, also considering the Ghasts and horrible terrain of the Nether.
Attacking one Zombie Pigman causes the whole group of nearby Zombie Pigmen to become hostile and attack the player, like wolves. Zombie Pigmen won't become neutral again unless they're killed, they won't become neutral even if the player dies, regardless whenever the death was caused by the pigman or not; however, they are faster than a walking player (speed of .95 Blocks Per Second is the enraged zombie pigman's speed) Setting the Game Mode to Peaceful removes all Zombie Pigmen, unlike wolves. If the player is attacked by a group of Zombie Pigmen, escapes through a Portal, and returns to the Nether soon afterward, the Zombie Pigmen will remain hostile. Since Update 1.4, Zombie Pigman have the ability to pick up weapons and armor of any defeated players.
In pocket edition, unlike the PC version, Zombie Pigmen spawn from a Nether Reactor. They will attack the player immediately. However, unlike the PC and the Xbox Edition, they do burn in the sun like zombies and skeletons.
Zombie Pigmen are incredibly strong, which gives them an unfair advantage to an unprepared player. If the player is in multiplayer, a zombie pigman that has been harmed will be aggressive towards all players (even players that did not harm the pigman). Zombie pigmen spawn in the Nether and the overworld, near any active Nether Portals and when a pig is struck by lightning. If a zombie pigman is harmed by another mob, the zombie pigman that was harmed will become hostile towards the mob that harmed it, but the rest of the group will remain neutral.
However, if an iron golem attacks a pigman, only that zombie pigman will be hostile.