Sir Bradley Wiggins and Chris Froome are among five British athletes to have their confidential health records leaked online.
The World Anti-Doping Agency (WADA) confirmed the leak from their databases by hackers - the second attack in a matter of days.
On Tuesday, Russia-based cyber-espionage group "Fancy Bear" disclosed details about US athletes Serena Williams and Simone Biles.
Two days later, WADA confirmed a second leak, which included details of Wiggins, Froome and three other British athletes.
Medical records leaked relate mainly to "therapeutical use exemptions" granted to certain athletes.
Leaked records show eight-time gold medalist Wiggins was allowed to take two banned substances - including during the 2011 Tour de France and the 2013 Giro d'Italia.
One of the substances, triamcinolone acetonide, was taken for an allergy to pollen.
Froome was permitted to take the banned steroid prednisolone on occasions between 2013 and 2014, including during the 2014 Tour of Romandy race.
The other British athletes who had details leaked were golfer Charley Hull, rugby sevens player Heather Fisher and rower Sam Townsend.
Other countries to be affected by the leak included the US, Germany, Czech Republic, Denmark, Poland, Romania and Russia.
WADA revealed that hackers had illegally gained access to its anti-doping administration and management system database via an International Olympic Committee-created account for the Rio Games.
WADA director general Olivier Niggli described the leak as a "criminal attack".
He regretted that hackers had attempted to "smear" the reputation of the athletes affected.
Mr Niggli said there was "no doubt" the leaks were being carried out because of investigations into 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.