UNITED NEWS INTERNATIONAL (UNI) — The official Winter Olympics website was hacked during the opening ceremony last week.

Officials confirmed the site was down for 12 hours, starting just before the ceremony began in Pyeongchang, on Feb. 9.

The game’s organizers say that no critical part of their operations was compromised and their operations are secure. The hack also affected the wifi in the Pyeongchang Olympic Stadium, as well as televisions and the internet in the main press center.

The International Olympic Committee has not confirmed who hacked the site. News sources, however, are reporting rumors that Russia is responsible. The Russian Foreign Ministry has denied the rumors.

Experts have been warning for the last few months that the games could be targeted by cyber-attacks. The U.S. Department of Homeland Security even published a warning to travelers about the risk earlier this month.

The IOC says the investigation is ongoing.