1. [Unix] A process that has died but has not yet relinquished its process table slot (because the parent process hasn't executed a wait(2) for it yet). These can be seen in ps(1) listings occasionally. Compare orphan.
2. A machine, especially someone's home box, that has been cracked and is being used as part of a second-stage attack by miscreants trying to mask their home IP address. Especially used of machines being exploited in large gangs for a mechanized denial-of-service attack like Tribe Flood Network; the image that goes with this is of a veritable army of zombies mindlessly doing the bidding of a necromancer.