Hackers attacked the opening ceremony of the Winter Olympics. The question is who they were.

Winter Olympics officials say that the games were struck by cyberattacks during the opening ceremony on Friday — but they won’t say who they believe could be behind them for now.

The official Pyeongchang 2018 website went down hours before the opening ceremony, making it impossible for customers to print tickets or look up the events schedule. It took 12 hours for the site to get back online.

And at the Pyeongchang Olympic stadium, where the opening ceremony was held, wifi went down and televisions in the press center stopped working, according to the Guardian.

On Sunday, a Winter Olympics official confirmed that cyberattacks cause those incidents, although he maintained that nothing critical had been affected by the attacks.

He also declined to comment on who could be behind the attacks, although it appears they may know who it could be.

“We know the cause of the problem but that kind of issue occurs frequently during the games. We decided with the IOC we are not going to reveal the source [of the attack],” Pyeongchang organizing committee spokesperson Sung Baik-you told reporters on Sunday. “We wouldn’t start giving you the details of an investigation before it is coming to an end.”

For now, experts believe there are two main suspects — and it shouldn’t be hard to guess who they are.

In the run-up to the Pyeongchang Olympics, cybersecurity firms and researchers predicted that Russia or North Korea might use cyberattacks to sabotage the Olympics.

North Korea and South Korea have spent decades sparring over Pyongyang’s nuclear weapons program, but the chilly relationship has thawed a bit after North Korean leader Kim Jong Un decided to send athletes to the games and dispatched his younger sister to accompany them. Kim Yo Jong has garnered enormous attention in South Korea for her outwardly relaxed and friendly demeanor.

Russia has an obvious motive to meddle in the Olympics: revenge. The International Olympic Committee formally banned Russia from the Pyeongchang Games as a punishment for the Russian government’s massive doping scheme that allowed Moscow to improperly win medals at the past two Olympics.

The International Olympic Committee set up a special screening process to determine if Russian athletes eligible for the Winter Olympics had violated anti-doping rules. That screening process barred scores of Russian athletes from the Games, and the 169 Russian athletes who did pass it are competing under a special status — as neutral “Olympic Athletes from Russia.” They can’t wear their country’s colors and any medals they win won’t go toward Russia’s medal count in the history books. Russia denies the existence of state-backed doping and has sharply criticized its exclusion from the Olympics.

Cybersecurity firm Trend Micro said that a hacking group with ties to Russia targeted the International Ski Federation and other sports organizations with links to the Winter Olympics with malicious emails recently.

Prior to the opening ceremony, Russia seemed to anticipate future accusations of cyberattacks.

“We know that Western media are planning pseudo-investigations on the theme of ‘Russian fingerprints’ in hacking attacks on information resources related to the hosting of the Winter Olympic Games in the Republic of Korea,” Russia’s Foreign Ministry said in a statement on Wednesday. ”Of course, no evidence will be presented to the world.”