Hackers leak details of Olympic athletes including Simone Biles and Serena Williams

A hack in which the personal details of high-profile Olympic athletes such as Simone Biles and Serena Williams were leaked has been condemned as "cowardly and despicable".

Hackers Tsar Team (APT28), who are also known as Fancy Bears, claim to have hacked a World Anti-Doping Agency (WADA) database and released information concerning substances for which athletes have sought and received therapeutic use exemption (TUE).

TUE medications are granted if an athlete requires a medication which falls under the Prohibited List to treat and illness or condition.

The hacks - which are understood to have originated in Russia - have so far targeted the US Olympic team, though Fancy Bears have promised to disclose the information of other teams in the future.

US Anti-Doping chief Travis T Tygart described the attack as an attempt to "smear" clean athletes.

The leak of four-times Olympic gold medalist Simone Biles' data revealed that she takes medication for Attention Defecit Hyperactivity Disorder (ADHD).

The 19-year-old hit out at the hackers in a series of posts on Twitter.

Speaking about Biles, Steve Penny, president of USA Gymnastics, said: "Simone has filed the proper paperwork per USADA and WADA requirements and there is no violation. The International Gymnastics Federation, the United States Olympic Committee and USADA have confirmed this."

The attacks are understood to have originated in the wake of the McLaren Report, which uncovered a state-sponsored doping programme in Russia and led to some athletes being banned from the Rio Olympics, with the country's entire Paralympics team being banned from this summer's games.

Former Wimbledon champion Venus Williams also saw her details leaked, along with her sister Serena Williams'.

The Rio mixed-doubles silver medalist said she was "disappointed" that her medical data has been "compromised by hackers and published without...permission", and that in applying for TUEs she had followed "a strict process of approval which I have adhered to when serious medical conditions have occurred".

WADA director general Olivier Niggli said: "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 added that it was taking the current situation "very seriously", and was carrying out security checks and working with law enforcement authorities to protect users of the hacked database.