Servers for Ubisoft's PC-based Uplay servers went down this morning, causing players of the newly released in Europe Far Cry 3 to be locked out of the game, lest they set Uplay to offline mode (something the game, service, and even Ubisoft doesn't suggest).
In any case, about hours three hours later, the issues have been fixed, so you can play as normal with no fiddling about required.
"Dearplayers, thank you for your patience, our servers are back up & running. Have fun playing!" the latest tweet from Ubisoft reads.