Ubisoft, one of the larger video gaming companies out there, has a somewhat troubled history of overburdening its games with awful DRM.
And, as with most DRM systems, the people it tends to hurt most are the legitimate purchasers who somehow run afoul of whatever DRM rules are in place.
In this case, the Ubisoft game Rainbow Six: Vegas2 (R6V2) had some DRM that would check to see if the physical media (CD-ROM) was in the drive before it would let you play.