The networks, which allow users to play video games with a wider audience online, suffered problems Thursday that continued Friday morning, angering thousands of gamers, many who tried using their brand-new consoles on Christmas.
The hacking group "Lizard Squad" took credit for the outages. The group previously claimed responsibility for cyber-attacks that briefly knocked the Vatican's website, Battle.net and League of Legends offline.
Neither Microsoft nor Sony blamed the problem on hackers. Both companies said they were investigating the problems.
Earlier this month, the Lizard Squad claimed it hacked Sony's PlayStation Store.
Sony has faced several hacks this month, with U.S. officials linking North Korea to one that disrupted the company's computer system and leaked confidential information online believed to be retaliation for Sony's original plans to release "The Interview," a comedy that featured a fictional assassination attempt against North Korean leader Kim Jong-un.