Simone Biles’s name came up Tuesday as among those of prominent female U.S. athletes revealed to have received exemptions for substances normally banned by the World Anti-Doping Agency. The Olympic gymnastics champion responded by acknowledging that she has attention deficit hyperactivity disorder (ADHD), saying on social media that it is “nothing to be ashamed of.”

In a pair of Twitter posts, Biles said that she believes “in clean sport,” and that she has “always followed the rules.” She, along with Elena Delle Donne and Serena and Venus Williams, had confidential information stored in the WADA database made public, following a computer hack the agency blamed on a Russian group linked to that country’s government.

The release of the information was apparently intended to sow suspicions about U.S. athletes, including Rio gold medal winners Biles and Delle Donne. The International Olympic Committee banned nearly the entire Russian team from this year’s Games, following investigations into an allegedly wide-spread, government-run doping program.

However, the confidential documents showed that the athletes had received “therapeutic use exemptions” (TUEs) from WADA, enabling them to use specified substances that are permitted only when athletes can prove, ahead of drug tests, that they are needed for certain medical conditions.

“Simone has filed the proper paperwork per [U.S. Anti-Doping Agency] and WADA requirements, and there is no violation,” Steve Penny, president of USA Gymnastics, said in a statement. “The International Gymnastics Federation, the United States Olympic Committee and USADA have confirmed Penny’s statement. Simone and everyone at USA Gymnastics believe in the importance of a level playing field for all athletes.”

“It’s unthinkable that in the Olympic movement, hackers would illegally obtain confidential medical information in an attempt to smear athletes to make it look as if they have done something wrong,” said Travis T. Tygart, head of USADA. “The athletes haven’t. In fact, in each of the situations, the athlete has done everything right in adhering to the global rules for obtaining permission to use a needed medication. … The cyber-bullying of innocent athletes being engaged in by these hackers is cowardly and despicable.”

“WADA deeply regrets this situation and is very conscious of the threat that it represents to athletes whose confidential information has been divulged through this criminal act,” WADA Director General Olivier Niggli said in a statement. The agency pinned the breach on a hacking group known as Fancy Bears, or APT28, which is connected to the Russian military intelligence service GRU. On a website, Fancy Bears claimed that it would “start with the U.S. team which has disgraced its name by tainted victories” and “also disclose exclusive information about other national Olympic teams later.”

“I was disappointed to learn today that my private, medical data has been compromised by hackers and published without my permission,” Venus Williams, who disclosed in 2011 that she suffers from Sjogren’s syndrome, said in a statement (via the Associated Press). She added that she has been granted a TUE while following “the rules established under the Tennis Anti-Doping Program.”

Like Biles, Delle Donne took to Twitter on Tuesday to respond to the revelation of confidential information. She posted a photo of herself in a hospital bed, with a bandage on her left hand from thumb surgery that day, and noted in a caption that she was taking medication for which she was granted a WADA exemption. “Thanks, guys!” she sarcastically added for the hackers’ benefit.