So Ubisoft has a rather checkered history in the public view for the PC in recent times and by checkered i mean either grey or black hole.
Going back to the first DRM Ubisoft was using, StarForce. StarForce was known to have a number of issues from causing hardware problems on the PC to even simply not being compatible with certain Operating Systems.
Now we move onto the DRM that took over from StarForce, Uplay. Uplay is always-online DRM which is always an issue because you can't always have the internet available, this means that even though you legitimately bought your game, you can't play it. This applies even if your net drops while you're playing the game, if it does then the game will stop playing and pause. The no connection = no play is also true if Ubisofts servers go down which has been an issue a number of times where people haven't been able to play their games due to Ubisoft servers being out of action.