If you've tried to play Hearthstone or World of Warcraft today, you've likely run into a Battle.net login queue that's a lot longer than you're used to. Blizzard says it's aware that something is amiss, and is now investigating the cause of the trouble.
Reports of overlong Hearthstone queues turned up earlier today on Reddit, where users complained of wait times of 15 minutes or more. Several posters suggested the problem bears the hallmarks of a DDoS attack, and while Blizzard hasn't acknowledged that this is the case, the "maintenance alert" message on Battle.net suggests that something untoward is happening.
"We’re aware of an issue that is affecting our authentication servers, which may result in failed or slow login attempts," it says. "We’re currently investigating the cause and will provide updates as they’re available."
One possible scenario is that this is another attack by "Lizard Squad," the group that brought so much grief to Xbox Live and PlayStation Network users over the holidays. It carried out a prior DDoS attack against Battle.net and other services in August 2014, when it also (and more famously) used a fake bomb threat to divert an American Airlines flight carrying Sony Online Entertainment President John Smedley.
We've reached out to Blizzard for more information and will update if and when we receive a reply.