LOS ANGELES (AFP) - The World Anti-Doping Agency (Wada) announced on Tuesday that its database had been hacked.
The hackers group released information gleaned from the confidential files of Olympic gymnastic star Simone Biles, tennis superstars Venus and Serena Williams and US women's basketball player Elena Delle Donne.
In a statement, Wada blamed the Russian cyber-espionage group Tsar Team (APT28), also known as Fancy Bears, for breaking into its Anti-Doping Administration and Management System (ADAMS) database.
So who are Fancy Bears?
Experts believe it is a Russian cyber-espionage group that has been tied on multiple occasions to breaches against government agencies, non-profit agencies and corporations.
According to the New York Times, that group is believed to be associated with Russia's military intelligence agency, the same organisation suspected of being involved in the recent theft of e-mails and documents from the Democratic National Committee.
On their website, Fancy Bears hinted that they are part of the global Anonymous collective, writing: "We are Anonymous. We are Legion. We do not forgive. We do not forget. Expect us. Anonymous - #OpOlympics"
According to the New York Times, the two groups had not been aligned before.
The hacking comes after a series of Wada investigations which have alleged a vast state-sponsored doping programmed 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.
The International Paralympic Committee also banned the entire Russian contingent from the ongoing Rio Games.
Anonymous has made a name in recent years for its unusual tactics such as taking websites offline such as that belonging to the US' Central Intelligence Agency and embarrassing major global players such as Sony.
Even Singapore was not immune, with a member of the collective called "The Messiah" hacking several sites in the country in 2013, as a protest against censorship and as a show of support for "a free and open Internet".
That year, websites with at least 50,000 unique visitors from Singapore every month that publish at least one local news article per week over a period of two months were required to obtain an annual licence.
The websites targeted included those of the PAP Community Foundation, Ang Mo Kio Town Council and three linked to City Harvest Church.
Many were defaced with taunts or threats.
A Straits Times blog was also targeted.
In January 2015, James Raj Arokiasamy, was jailed for four years and eight months yesterday, after pleading guilty last week to 39 charges of computer misuse.