The Atari Forums (thanks HomeLAN Fed and Planet Unreal) has a post from Epic programmer DrSiN on their intentions of seriously pursuing cheaters and thieves of CD keys:

In addition to an improved version of the cheat-stopping measures found in UT2003, UT2004 utilizes a targeted tracking and response system at the master server level that allows us to focus on those people really causing problems. Yesterday we identified and permanently banned a UT2004 player, "Zellius", for cheating.

We have had reports of people trying to gain access to other paying customers' CD keys. Please use common sense. Don't send anyone screenshots or dumps of the registry entries showing your key. Don't download "hacks" because they may contain a CD key stealer, or worse.

No one from Epic, Digital Extremes, or Atari will ever approach you and ask for your CD key. You will only be asked for your unique ID in the Game tab of your settings menu.

CD key theft is a crime against a UT2004 customer. We will hand over any evidence of key theft to Atari's legal department for immediate action.