Assassin's Creed has the stupidest DRM ever
The game requires a constant connection to the internet. So that means if, while you are playing in single player mode, your internet connection drops for any reason, the game instantly boots you out to a menu and discards all progress that you've made up to that point. Similarly, if the Ubisoft servers have any issues, it also instantly boots you to the menu screen.
As the people over at RPS comment, "It’s like someone taking away your food mid-meal because your napkin’s fallen on the floor"