A hacker group called the Lizard Squad has claimed responsibility for taking down the PlayStation Network in North America today, according to reports.

Sony tweeted its engineers were working on bringing the gaming network back up. The Japanese tech giant also did not issue a time frame for when it would be able to restore all the services. They were not immediately able to verify Lizard Squad’s claims or how the hackers were able to execute the attack.

The hacker group has reportedly also attacked servers for Blizzard’s top games World of Warcraft, Diablo 3, and Hearthstone, VentureBeat reported citing ShackNews.

This weekend’s attack was the worst breach of PlayStation’s vaunted network since 2011, when hackers were able to access data of more than 12.3 million PSN account holders.

The network was partially restored for some users by 10 am Pacific Time with partial services including Netflix back on, according to IGN.

The attack was due to denial-of-service, commonly referred to as DDoS, attack, the site said.

Sony President of Online Entertainment John Smedley tweeted about the attack shortly after it occurred Sunday morning.