In a statement released Monday, the IAAF said the cyber attack which took place in February focused on athletes who had made applications for Therapeutic Use Exemptions (TUEs).
On Monday the IAAF - athletics' global governing body - released a statement to say it had now suffered a "cyber attack" which was discovered following a "proactive investigation" by an online security firm contacted by the body in January.
IAAF has not confirmed a subsequent intrusion by hacker to its servers, while admitting that it has showed the attackers' interest and intent, and their access and means to obtain content from the file at will.
The organization reached out to all of the athletes who had applied for TUEs since 2012, providing them with an e-mail address for any questions they might have regarding this incident.
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The IAAF issued a statement on Monday saying they, over the last one month, consulted the UK National Cyber Security Centre (NCSC) and the Agence Monégasque de Sécurité Numérique (Monaco AMSN) "and worked with Context to carry out a complex remediation across all systems and servers in order to remove the attackers' access to the network".
The International Association of Athletics Federations (IAAF) president Sebastien Coe has apologised to athletes.
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"They have our sincerest apologies and our total commitment to continue to do everything in our power to remedy the situation and work with the world's best organisations to create as safe an environment as we can".
The attack was uncovered after British company Context Information Security conducted a investigation of the IAAF's systems at the request of the athletics body.
The same cyberespionage group claimed responsibility for leaking Olympic athletes' confidential medical files following an attack against the World Anti-Doping Agency a year ago and has been linked to interference with the U.S. election in 2016.
In December, it was revealed Fancy Bears' had been named in a United States security services report into cyber bodies linked to the Russian Intelligence Services.
Russian hacking crew APT 28 (aka Fancy Bears) attacked the World Anti-Doping Agency database last September before leaking athletes' confidential details, including TUE-based permissions to take prohibited substances because of a medical need.
As of today, Fancy Bears' website contained no mention of IAAF information.