Exorcism is one of the few ranged attacks available to Paladins.
Patch 3.2.0 (04-Aug-2009): Now has a 1.5 second cast time, but can once again be used on players.
Patch 3.1.1a (2009-04-28): "..fix[ed] the tooltip to display the appropriate text; it also displays an error message when a player tries to use it against other players."
Patch 3.1.1 (2009-04-21): "..the paladin ability Exorcism cannot damage other players, but the player game client does not display this change properly."
Patch 3.1.0 (14-Apr-2009): Exorcism: Now can be used on any target and has a 100% chance to be a critical strike when used on Undead and Demons. This is to ensure that paladins do not see a drop in their dps when progressing from Naxxramas (which is full of undead) to Ulduar and beyond (not as much undead). Due to this change, [Glyph of Exorcism] was changed to 20% bonus damage.