Developer DICE has confirmed
that ongoing denial of service attacks on the server infrastructure for Battlefield 3 are behind the disruptions to the game's multiplayer component over the last several days.
Despite our security measures, we have been working around the clock to mitigate the impact of an ongoing denial-of-service attack on our Battlefield 3 game infrastructure over the last several days. While the motives are unclear, the focus of the attack has been interference with network communications preventing access to multiplayer gameplay. At this point, no user data is involved. We share your frustration about the impact this has had to our service and the ability for many of you to play Battlefield 3. We are working tirelessly to mitigate the problem.
Although the games servers themselves are hosted by third party companies around the world, their operation is dependent on centralised infrastructure of the Battlelog service for cheat protection, game stat tracking and persistent item unlocks.