Sony's PlayStation and Microsoft's Xbox were partially inaccessible to users on Wednesday and Thursday, as frustrated holiday gift recipients discovered they were unable to connect with the gaming networks.
Microsoft issued a service alert, warning that that signing into Xbox Live has been impacted, saying:
Are you having difficulties signing in to Xbox Live? We're working to address this as quickly as we possibly can! Thanks for your patience, Xbox members. We'll have an update right here in 30 minutes.
Sony also acknowledged on Twitter that its network was having access issues.
An obscure hacker group calling itself Lizard Squad has been claiming responsibility for both attacks on Twitter.
Myriad furious tweets by gamers unable to play put the blame squarely on the hacker group.
Earlier this year, Lizard Squad warned that explosives might be on a flight that included a Sony executive among its passengers, and claimed responsibility for a disruption to the PlayStation network. American Airlines diverted the domestic U.S. flight to a nearby airport.
In that incident, hackers orchestrated a so-called denial-of-service attack against Sony, which involved overwhelming the company's game network with fake visits so that legitimate users couldn't get through.
—The Associated Press contributed to this report.