Sony says its PlayStation Network is back online after three days of disruptions that began on Christmas.

But heavy traffic might continue to cause problems for customers seeking to play their favorite games, the company said Sunday.

A group of hackers called Lizard Squad — or someone claiming to speak for it — took credit for the disruptions. In a blog post Saturday night saying service had been restored, Sony vice president Catherine Jensen added that “PlayStation Network and some other gaming services were attacked over the holidays with artificially high levels of traffic to disrupt connectivity and online gameplay.”

Microsoft’s Xbox Live service, which also went down Thursday, was back online Friday, although the company reported continuing problems.

So far, there’s no evidence to link these episodes with last month’s attack on Sony Pictures Entertainment. The FBI has blamed that attack on North Korea, which was furious about Sony’s “The Interview,” a movie comedy about a plot to assassinate North Korean leader Kim Jong Un.