Sony is currently investigating problems causing users to experience difficulties logging in, according to a tweet from PlayStation's official Twitter account.
We're aware that some users are having issues logging into PSN - engineers are investigating— PlayStation (@PlayStation) December 25, 2014
Further details, including a time frame to fix this problem, were not provided. According to PlayStation's support page, PSN is currently online. The network was experiencing issues last night as well, though an update promised the company would continue to monitor its status.
For almost a month, two groups of self-described hackers have been fighting over a threat to take down both the PlayStation Network and Xbox Live on Christmas Day. Lizard Squad, a group that claims responsibility for previous network outages and diverting Sony Online Entertainment head John Smedley's flight in August, also promised to launch the Christmas Day attack. The Finest Squad — the group opposing such threats — says it will be working against those attacks.
The current problems on PSN have not been linked with either group so far.
At the time of this post, Xbox Live appears to be functioning normally in its core services; apps such as IGN, Maxim and MLG.TV are noted as having limited service. In a comment given to Polygon previously, Microsoft said it takes "the security of our customers' data very seriously" and has professionals monitoring and managing the security of its services.
Update: It appears Xbox Live is currently experiencing outages as well.
"Unable to sign in to Xbox Live?" the support page reads. "We're already hard at work trying to reach a solution as soon as possible. Thanks for hanging in there in the meantime."
Update 2: On Twitter, Lizard Squad is claiming credit for the downtime on both PSN and Xbox Live. Sony and Microsoft have not confirmed or commented on these claims.