Uplink Hints

What's this three-letter combination that I keep finding in the forums?

  • 1 of 3: Due to the fact that I've seen absolutely too many posts in the Uplink Forums containing this simple question, I've decided to put this here.
  • 2 of 3: It is a hint (way too big a hint) for the Introversion Machine.
  • 3 of 3: I'm talking, of course, about 'ABH'.