It has already been reported that GTA 4 PC would possibly require an online activation. Those rumors have been confirmed now. But Rockstar uses, in contrast to Electronic Arts' DRM system (Spore, C&C Red Alert 3) or Ascaron (Sacred 2), a less rigid solution. Here the summary of the GTA 4 DRM system:

DRM system GTA 4 (PC):
- Activation via Internet (1x per system, no limits, Fallback for systems without web access)
- Copy protection Securom: The original disc is required for playing (Exept: Download version of GTA 4, for example from Direct 2 Drive)
- Requirements for playing (singleplayer): original disc, Securom and GFW Live runs in the background
- Requirements for playing (multiplayer): Active internet connection, Games for Windows Live account, For uploading videos: Rockstar Social Club Account

Additional details about the activation of GTA 4 (PC):
- If you don't have web access or don't want to connect your gaming PC to the Internet, Rockstar wants to offer a not yet specified system to activate GTA 4 via another PC with web access. Details are supposed to be available on launch.
- For the normal GTA 4 (PC) version with disc installation, activations are unlimited. But the original disc is required for playing.
- This does not apply for legally downloaded versions of GTA 4: Depending on the vendor the following is possible: Five parallel installations with the possibility to revive a "free” installation, if an old installation is deleted. For this purpose the customer has to have web access with the PC GTA 4 is installed on.
- Those playing GTA 4 with an illegally hacked version have, according to Rockstar, to fear that the game will not be fully playable.
- If you change two major components of your PC (like the graphics card or the CPU), you will possible have to reactivate GTA 4.

On page two you can find the full Rockstar Q&A, if you have any further questions. Our opinion: The unlimited number of installations for the normal retail version is a step on the right track.