Serena Williams, one of the world's greatest ever tennis players, was taking a number of banned substances

A hacktivist group claims it has uncovered files that show top American athletes including Serena Williams and Simone Biles took banned substances - although their respective sporting federations responded by saying the athletes did not break any rules.However, the documents released also showed that Williams had been given special permission to take some of the drugs. The authorization was given by Dr. Stuart Miller from the International Tennis Federation (ITF).. However, she was given special dispensation to take the substances as long as she adhered to various conditions regarding the use of the drugs.RT has contacted the International Federation of Gymnastics for comment, with its representative saying the body followed the current rules and that there is "no problem.""She [Biles] has a therapeutic use exemption, there is nothing we have to mention about that, everything is absolutely clear and according to the rules."WADA has released a statement confirming the cyber attack. It noted that the cyber intrusion was conducted by a Russian hacker team and that it is taking the attack "very seriously.""The group accessed athlete data, including confidential medical data - such as Therapeutic Use Exemptions delivered by International Sports Federations (IFs) and National Anti-Doping Organizations (NADOs) - related to the Rio Games."According to the body, the information was obtained "through spear phishing of email accounts."An internal investigation has been launched, WADA said in the statement.