Last year the DRM (Digital Rights Management) system employed in Splinter Cell: Conviction and Assassin's Creed: Brotherhood was faced by a strong backlash from gamers and critics who were not too pleased by the fact that it required constant internet connection while playing the single player campaign.
In January 2011 Ubisoft heeded to the gamer's dissent and removed that DRM from the games that used and everybody thought that this was the end of the story. Unfortunately, Ubisoft decided to use that DRM again in its upcoming Driver: Sand Francisco.
The reason given by Ubisoft for using such an anti-user system again is that it is effective. The company spokesperson has said that they have seen "a clear reduction in piracy of our titles which required a persistent online connection, and from that point of view the requirement is a success."
Oddly enough, said DRM was cracked within a few days of the games' release; even more, hackers prevented legitimate players from playing for extended periods by taking down the DRM's authentication server.
Despite deeming it a success, Ubisoft isn't going to use the always-online DRM in all its games as the company has already confirmed that its upcoming From Dust won't employ it.