From what can be confirmed through various alien captive recorded logs, abominations are captured human test subjects whose bodies have been hybridized with alien DNA with the intention of creating biological weapons. The transformation process turns the subjects into feral, menacing creatures - hostile to anything that is not one of them, including their alien creators - and removes all discernible sexual characteristics, leaving them with an androgynous appearance. Despite this, it is evident that these creatures retain some degree of their humanity and self awareness; when killing an abomination, sometimes they are known to say "thank you", as if to suggest that they had wanted to die all along. It is unknown if there are more of them on the ship after finishing the Mothership Zeta add-on.
Their known creation history and asexual appearance seems very similar to super mutants, while their hostility and lack of self-preservation are reminiscent of feral ghouls. Super mutants and feral ghouls both "evolved" from humans, and specimens of both species can be found in the alien cryo labs.
After spotting a target, an abomination will point at it and wail loudly, and then attack with its long arms (in a manner that is very similar to feral ghouls), making them difficult to engage with unarmed or melee weapons. Abominations are a fairly standard opponent, and are easily killed with alien weapons. When killed, their bodies often contain various conventional alien items, such as alien power modules or alien epoxy. Sometimes, however, they contain items commonly found on the bodies of feral ghouls, such as packs of cigarettes, pre-War money, harmonicas and other miscellaneous items, which serve to reinforce the abominations' human origin. In a few rare cases they have also dropped pre-War books.
Upon being killed, an abomination can sometimes be heard saying "thank you," indicating that it wanted to die. The Pitt's trogs also sometimes utter the same remark when dying. However, no change in Karma results from killing one.
The way that the abominations point and screech when they notice the player is a reference to the 1978 remake of the movie Invasion of the Body Snatchers, in that the alien "pod-people" point and screech in the same way whenever they discover a real human.