The World Anti-Doping Association's (WADA) database has been under attack for weeks, its president Craig Reedie told the BBC on Wednesday.
Reedie's remarks came a day after WADA revealed the Russian cyber-espionage group Tsar Team (APT28), also known as Fancy Bears, had broken into its Anti-Doping Administration and Management System (ADAMS) database.
The hacking group released information gleaned from the files of US Olympic gymnastic star Biles, tennis legends the Williams sisters and US women's basketball player Elena Delle Donne, claiming US athletes at the Olympics had 'played well but not fair'.
Reedie, who is also a senior member of the International Olympic Committee (IOC), said there was little doubt despite denials by the Russian government the hackers came from Russia.
"We have pretty authoritative information that they have close connections to Russia," said Reedie.
"They have been attacking our system now for weeks.
"We have been under attack for weeks. This is an attack on the anti-doping system. and it's rather unhelpful at the moment," added Reedie in reference to the ongoing efforts to bring Russia into line after the damning WADA-commissioned independent report that revealed state sponsored doping dating back to the 2013 World Athletics Championships and the 2014 Sochi Winter Olympics.
"Russia have claimed at the very highest level that they understand they have a problem, but they still seem in some ways to be in denial. If we have to make the biggest country in the world compliant in anti-doping terms, then this is distinctly unhelpful."
- 'Hacking has to stop' -
Reedie, whose body advocated a ban on all Russian athletes at the Rio Games before the IOC controversially ruled federations should decide on the eligibility of each one in their respective sports to compete, said the hacking had to stop.
The Fancy Bears have threatened to release more files saying those already published were just the 'tip of the iceberg'.
"I hope the court of world opinion will see that this is an attack on the system, that it is unwarranted and that it has to stop," said Reedie.
None of the documents published by the group provided evidence of wrongdoing on the part of the athletes involved.
Instead, the disclosed files set out instances where the athletes had been granted exemptions to use various medications for legitimate reasons -- a common practice in the sports world.
Reedie confirmed this saying there was nothing sinister in the details that had been revealed.
"There is a long-established system of therapeutic use exemptions whereby an athlete who requires to take medicine that may be on the prohibited list can get an exemption to do so, provided it is certified properly by medical people and then certified by the relevant international federation," said Reedie.
"As far as I can see in the cases that were mentioned, all of that has been done, and has been done correctly," added the Scotsman.
WADA said it believed the latest breach had occurred after "spear phishing" of email accounts and that it had been confined to ADAMS accounts of athletes competing in Rio.
Spear phishing is when an email user receives a message purportedly from someone they know, but it is actually from a hacker.
The data breach comes just weeks after hackers gained access to WADA's file on Russian doping whistleblower Yulia Stepanova.
Stepanova, who is living in hiding in the United States, later said she feared for her life following the hack.
The latest incident comes after a series of WADA investigations which have alleged a vast state-sponsored doping programme in Russian sport dating back several years.
Russia's track and field athletes were banned from the Rio Olympics by the International Association of Athletics Federations, angering the Kremlin, which condemned the move as politically motivated.
But an independent report commissioned by WADA and published in July by Canadian law professor Richard McLaren concluded Russia had run an elaborate scheme to evade drug-testers at the 2014 Winter Olympics in Sochi, corroborating claims by the former head of Russia's anti-doping laboratory.
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