Russian whistleblower Yulia Stepanova's electronic account at the World Anti-Doping Agency has been illegally accessed, WADA said on Saturday.
The anti-doping body said a "perpetrator" had illegally obtained the password for the middle-distance runner's account, and accessed details which would normally include her registered whereabouts.
"The World Anti-Doping Agency (WADA) confirms that Yulia Stepanova’s password for WADA’s Anti-Doping Administration and Management System (ADAMS) was illegally obtained, which allowed a perpetrator to access her account on ADAMS," WADA said in a statement.
Stepanova, in hiding in North America, helped reveal the biggest state-backed doping programme in Russia and was forced to flee the country with her husband for fear of her life.
As a result Russia's track and field team has been banned from the Rio Olympics while all Russian competitors in other sports had to prove they were clean by meeting several criteria in order to be eligible to compete in Brazil.
"The Agency noted that someone, other than Ms. Stepanova, had accessed her account. WADA immediately locked Ms. Stepanova's account to prevent further access and notified her of the situation," WADA said.
"A subsequent investigation by WADA allowed the Agency to determine that no other athlete accounts on ADAMS have been accessed."
All athletes have to enter their details into ADAMS and register a time and location each day when and where they can be reached by doping testers in case of an out-of-competition test.
Stepanova, praised by the international athletics body (IAAF) for her courage in stepping forward and revealing details on widespread doping in Russia, is still an active athlete and had attempted to compete in Rio.
The International Olympic Committee, however, refused to admit her as a neutral athlete, as proposed by the IAAF.
WADA said the incident came just days after what it said was "an alleged hack" of their website with some users receiving e-mails that looked as if they came from WADA urging them to enter their credentials.
"WADA quickly investigated and immediately sent an e-mail to all ADAMS users, including a warning banner on the ADAMS home page, alerting them to these e-mails, which WADA would never send, and asking them to advise ADAMS support immediately if they were to receive such an e-mail."
Image: Yulia Stepanova of Russia competes
Photograph: Michael Kooren/Reuters