Bradley Wiggins, Chris Froome targeted by Russian hackers Fancy Bear

CNBC with Reuters
Bradley Wiggins competes in the Men's Team Pursuit Final at the Rio 2016 Olympic Games.
Bryn Lennon | Getty Images

British cycling stars Bradley Wiggins and Chris Froome are among the latest batch of athletes to have their confidential medical information released by a group of Russian hackers.

The hacking group Fancy Bears published the names and documentation of 25 athletes that it alleged had taken banned substances.

"We go on exposing the athletes who violate the principles of fair play by taking doping substances," the group said in a new entry, called WADA databases Part 2, on its website. It went on to promise new leaks.

The documents released, however, appeared to be related to "therapeutic use exemptions" (TUE) obtained by the athletes from various sporting bodies. TUEs allow competitors to take drugs in order to treat medical conditions; there is no suggestion of wrongdoing by the athletes.

This follows the release on Tuesday by the same hackers of TUEs belonging to celebrated U.S. gymnast Simone Biles, basketball player Elena Delle Donne and tennis superstars Serena and Venus Williams.

The World Anti-Doping Agency (WADA), which has previously revealed that the confidential information was stolen during a hack of its database, confirmed on Thusday that there had been another batch of information leaked by Fancy Bear, involving 10 U.S. athletes, 5 Germans, 5 Brits, and one each from the Czech Republic, Denmark, Poland, Romania and Russia.

Russian hackers leak Simone Biles medical data
Russian hackers leak Simone Biles medical data

American swimmers John Conger and Kathleen Baker, waterpolo player McQuin Baron, tennis player Bethanie Mattek-Sands, hammer-thrower Deanna Price, fencer Dagmara Wozniak, basketballer Brittney Griner, shot-putter Michelle Carter, diver Sam Dornan and wrestler Tervel Ivaylov Dlagnev were among those whose documents were allegedly released on Thursday.

The British athletes named included golfer Charley Hull, rugby union player Heather Fisher and rower Sam Townsend.

CNBC has not independently verified the legitimacy of the documents.

WADA said it believed the attacks were being carried out as retaliation for the agency's investigations that exposed state-sponsored doping in Russia.

"We condemn this criminal activity and have asked the Russian Government to do everything in their power to make it stop," WADA Director General Olivier Niggli said in a statement. "Continued cyber-attacks emanating from Russia seriously undermine the work that is being carried out to rebuild a compliant anti-doping program in Russia."

After the first leak, a spokesman for Russian President Vladimir Putin rejected any suggestion Russia had backed the hackers' actions.

"There can be no talk about any official or government involvement, any involvement of Russian agencies in those actions. It's absolutely out of the question," spokesman Dmitry Peskov said in a statement carried by Russian news agencies. "Such unfounded accusations don't befit any organization, if they aren't backed by substance."

Russia was stung after many of its competitors were banned from August's Rio Olympics, after WADA accused the country's sports ministry of overseeing a vast doping program of its Olympic athletes.

—Follow CNBC International on Twitter and Facebook.