Ubisoft has apparently quietly turned off it's "always on" DRM for PC users. Before the change, games like Assassin's Creed Brotherhood required an internet connection in order to function, so you were basically boned if you had spotty Wi-Fi or wanted to play on airplane or something.
The new changes to Ubi's DRM scheme now mean you must have a connection when you first boot the games up, in order that you can be verified as a customer, but after that, feel free to turn off your modem and play all day..
This is a step in the right direction for Ubi. While piracy is always bad, software companies instituting DRM schemes that penalize legit customers seems like a self-defeating strategy at a certain point. After all, if it's easier and less intrusive to play a pirated game, most people will opt for that, since it's free, too. It's hard to justify paying for something that's troublesome and bad, when the "easy" version is free.
Source: PC Gamer