More than a dozen teams in the US National Football League have had their social media accounts hacked.
The teams included the San Francisco 49ers and Kansas City Chiefs, who will compete in the Super Bowl Championship on 2 February.
The hacking group OurMine took responsibility for the attack, which said it was to show internet security was "still low" and had to be improved.
The Twitter, Facebook and Instagram accounts for 15 teams were compromised.
Twitter confirmed the accounts were hacked by a third-party platform.
"As soon as we were made aware of the issue, we locked the compromised accounts and are working closely with our partners at the NFL to restore them."
Some of the accounts had their profile pictures or headers changed or deleted.
In the past, the group has hacked the Twitter accounts of Netflix, Marvel, Google's chief executive Sundar Pichai, and Twitter's founder Jack Dorsey. It has also hacked Buzzfeed's website and multiple Facebook and YouTube accounts.
Throughout Monday the hacking group targeted the NFL's own Twitter account along with the accounts of the Kansas City Chiefs, Green Bay Packers, Dallas Cowboys, Denver Broncos, Indianapolis Colts, Houston Texans, New York Giants, Philadelphia Eagles, Tampa Bay Buccaneers, Los Angeles Chargers, San Francisco 49ers, Cleveland Browns, Arizona Cardinals and Chicago Bears.