The World Anti-Doping Agency (WADA) has indicated the hacker group Fancy Bears may have doctored or fabricated some of the medical documents of athletes that it has released.
WADA released an update on Wednesday into its own cyber security investigation, reporting that a Rio 2016 section of its anti-doping administration and management system (ADAMS) was accessed after a 'spear phishing' attack.
Such an attack involves tricking the recipient into giving away details such as usernames and passwords, and WADA said several of its and the International Olympic Committee's email accounts were targeted, giving hackers means to obtain the confidential records of Rio competitors.
A host of major names from world sport have seen personal information dumped into the public domain, including professionally cyclists Chris Froome, Bradley Wiggins, Fabian Cancellara, Jack Bobridge, Emma Johansson and Laura Trott, by hackers who are believed to be Russian.
Some of the information released may not be genuine, however, according to WADA.
"WADA has determined that not all data released by Fancy Bear (in its PDF documents) accurately reflects ADAMS data, The agency said in a statement. "However, we are continuing to examine the extent of this as a priority and we would encourage any affected parties to contact WADA should they become aware of any inaccuracies in the data that has been released."
WADA, in its update, said "multiple" visits by the hackers between August 25 and September 12 led to the leaking of private medical details that showed when therapeutic use exemptions (TUEs) were granted.
TUEs allow athletes to take medicine that otherwise would be banned by WADA, and stringent conditions apply to their use.
WADA said it had taken steps to tighten up security within ADAMS, including deactivating all Rio 2016 accounts and bringing in outside forensic experts to determine the degree of intrusion and quash any future threat.
The agency also said some ADAMS users have received rogue messages, which misleadingly appear to come from WADA deputy director general Rob Koehler, asking the recipient to speak to him regarding the cyber attacks.
WADA is based in Montreal, Canada, and oversees and co-ordinates sport's anti-doping efforts.
Wednesday's statement urged athletes with concerns about hacking to get in touch, and added: "WADA thanks athletes and ADOs for their understanding and support.
"WADA is taking this situation, concerning athlete privacy, very seriously and will continue to provide relevant updates as circumstances evolve."