The update also includes the highly objected addition of DRM to the game in the form of SecuROM. Listed on the Steam page for the DLC is that the update includes SecuROM and has a 5 machine activation limit.
However on the Gearbox store the DLC is listed as being
limited to 5 concurrent installations. There is a big difference between having a 5 time activation limit and being able to have 5 concurrent installs of the game at one time. At this point in time it’s not clear if the DRM restrictions are the same across all digital delivery services or not.
Feel free to discuss the addition of DRM to Borderlands as well as the recently released DLC, The Zombie Island of Dr. Ned, on our Borderlands forums.