The system requires any Ubisoft PC game to be have a permanent online connection to Ubisoft's servers in order to be played.
Blog author Tom Francis experimented with his review copy of Assassin's Creed II, and found that if he got disconnected while playing he was immediately booted out of the game and lost all the progress he'd made since his last save point.
Francis argues that this won't just inconvenience players with flaky internet connections or routers, but leave them at the mercy of Ubisoft's own servers too.
"We know this choice is controversial but we feel it is justified by the gameplay advantages offered by the system and because most PCs are already connected to the internet," Ubisoft said last month, pointing out that it allows "cloud" saving so you can play the game from any PC, and install it on as many systems as you like.
Blizzard's new Battle.net system, launching later this year with StarCraft II, also requires an internet connection, although it does offer an offline mode that only allows you to log in as a guest. With Battle.net, you won't be able to earn achievements or access your save games and player records while offline.
Assassin's Creed II for PC is released in Europe on 5th March. It comes with both DLC releases to date: the Battle of Forli and this week's Bonfire of the Vanities (watch out for a review very soon).