They originally claimed it was due to exceptional demand

UBISOFT: "Due to the overwhelming popularity of Assassin's Crfeed II and Silent Hunter 5, our servers were temporarily down yesterday"
GAMERS: "So, by your own admission your system doesn't work. Are we going to have these outages every time a new game is launched"
UBISOFT: "Actually it was hackers. Hackers took us down. Not demand. Hackers."
GAMERS: "So, by your own admission your system is vulnerable and can be taken down by malicious users. Didn't you say you'd patch it out if this keeps happening?"
UBISOFT: "Err.." thows smoke grenade, runs like hell