The World Anti-Doping Agency (WADA) said Tuesday that a Russian cyber espionage group was behind an attack on its database at the Rio de Janeiro Olympics.
WADA said in a statement it "confirms that a Russian cyber espionage group operator by the name of Tsar Team (APT28), also known as Fancy Bear, illegally gained access to WADA’s Anti-Doping Administration and Management System (ADAMS) database via an International Olympic Committee (IOC)-created account for the Rio 2016 Games."
The statement said the group accessed data from athletes, mainly confidential data around medical exemptions which allow athletes to use normally forbidden substances for therapeutic reasons.
According to the Fancy Bears website, the leaked data concerns, among others, tennis star Serena Williams, and gymnast Simone Biles who won four golds and a bronze in Rio.
The group pledged allegiance to the loosely associated Anomymous internet activist hacker group, saying "we stand for fair play and clean sport" and "we are going to tell you how Olympic medals are won."
WADA said access was likely obtained by gaining possession of passwords through spear phishing of email accounts.
"WADA has been informed by law enforcement authorities that these attacks are originating out of Russia,” WADA director general Olivier Niggli said.
"Let it be known that these criminal acts are greatly compromising the effort by the global anti-doping community to re-establish trust in Russia further to the outcomes of the Agency’s independent McLaren Investigation Report."
WADA investigator Richard McLaren said in his report in July that Russia conducted a wide-ranging and state-sponsored doping programme.
As a result, all Russian athletes have been banned from the current Paralympics, while Russia escaped a blanket ban from last month's Olympics.
But its entire athletics team apart from US-based long jumper Darya Klishina was banned from the Rio Games in connection two previous WADA reports.
These were based at least partly on information provided by whistleblower Yulia Stepanova and her husband who now live in a secret location in the United States.
Stepanova's Wada account was hacked in early August, and Niggli said: “WADA condemns these ongoing cyber-attacks that are being carried out in an attempt to undermine WADA and the global anti-doping system."
Looking at the latest attack, he 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.
"We are reaching out to stakeholders, such as the IOC, IFs and NADOs, regarding the specific athletes impacted."