The World Anti-Doping Agency on Tuesday slammed Russian hackers who breached its database and published confidential records of US Olympic gymnast Simone Biles and tennis stars Venus and Serena Williams.
WADA said in a statement that the Russian cyber-espionage group Tsar Team (APT28), also known as Fancy Bears, had broken into its Anti-Doping Administration and Management System (ADAMS) database.
The hacking group released information gleaned from the files of Biles, the Williams sisters and US women's basketball player Elena Delle Donne.
In a posting on its website, Fancy Bears claimed US athletes at the Olympics had "played well but not fair."
However none of the documents published by the group showed wrongdoing.
Instead, the disclosed files set out instances where the athletes had been granted exemptions to use various medications for legitimate reasons -- a common practice in the sports world.
The United States Anti-Doping Agency (USADA) characterized the hack as a "cowardly and despicable" attempt to smear the four women.
"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," USADA chief executive Travis Tygart said.
"The cyber-bullying of innocent athletes being engaged by these hackers is cowardly and despicable," added Tygart, the anti-doping czar who famously helped expose US cyclist and dope cheat Lance Armstrong.
- 'I believe in clean sport' -
Biles said on Twitter she had taken medications for attention deficit/hyperactivity disorder (ADHD) since childhood.
"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 is very important to me," said Biles, one of the stars of the Rio Olympics after winning four gold medals.
Venus Williams meanwhile expressed "disappointment" at the breach, stating: "I am one of the strongest supporters of maintaining the highest level of integrity in competitive sport."
An International Olympic Committee (IOC) spokeswoman said the leaked information was "clearly aimed at tarnishing the reputation of clean athletes" while stating that no anti-doping violation had occurred.