Hackers linked to the Russian government leaked the medical records of four US athletes including Serena Williams and Simone Biles.
The World Anti-Doping Agency confirmed Tuesday that a hacking group called Fancy Bear hacked its database of Olympians for the Rio games.
Last month, NBC News reported a suspected hack of WADA files. US officials believe the group is linked to Russia's military intelligence agency. The attack comes after Russia's athletes were banned from the Rio Olympics for doping.
Tuesday, WADA confirmed the hack and authorities have traced the hack to Russia.
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On their website the hackers posted information accusing Serena Williams of taking painkillers and anti-inflammatory medicine. Simone Biles was also targeted, with her records showing that she'd tested positive for methylphenidate in August.
The hack led Biles to proudly open up about having ADHD, which she takes medication for that includes methylphenidate.
"I have ADHD," she tweeted, "and I have taken medicine for it since I was a kid. Please know, I believe in clean sport, have always followed the rules, and will continue to do so as fair play is critical to sport and very important to me."
She added, "Having ADHD, and taking medicine for it is nothing to be ashamed of nothing that I'm afraid to let people know."
Russian officials have denied being involved in the attack. WADA Director General Olivier Niggli assured reporters that they are taking the hack seriously and working with law enforcement to investigate.