The World Anti-Doping Agency (WADA) has revealed that it has been hacked by a Russian cyber espionage group.

WADA on Tuesday confirmed that a database containing information, including confidential medical data, was accessed illegally in cyber-attacks that are "ongoing".

Russian track and field athletes along with some athletes from other sports were banned from competing in the Rio Olympic Games last month following an independent commission that found evidence of state-sponsored doping.

And WADA gave details of another twist in the doping scandal on Tuesday.

A WADA statement said: "The World Anti-Doping Agency (WADA) confirms that a Russian cyber espionage group operator by the name of Tsar Team (APT28), also known as Fancy Bear, illegally gained access to WADA's Anti-Doping Administration and Management System (ADAMS) database via an International Olympic Committee (IOC)-created account for the Rio 2016 Games.

"The group accessed athlete data, including confidential medical data -- such as Therapeutic Use Exemptions delivered by International Sports Federations (IFs) and National Anti-Doping Organizations (NADOs) -- related to the Rio Games; and, subsequently released some of the data in the public domain, accompanied by the threat that they will release more.

"While it is an evolving situation, at present, we believe that access to ADAMS was obtained through spear phishing of email accounts; whereby, ADAMS passwords were obtained enabling access to ADAMS account information confined to the Rio 2016 Games.

"At present, we have no reason to believe that other ADAMS data has been compromised."

WADA director general Olivier Niggli said: "WADA deeply regrets this situation and is very conscious of the threat that it represents to athletes whose confidential information has been divulged through this criminal act. 

"We are reaching out to stakeholders, such as the IOC, IFs and NADOs, regarding the specific athletes impacted.

"WADA condemns these ongoing cyber-attacks that are being carried out in an attempt to undermine WADA and the global anti-doping system. WADA has been informed by law enforcement authorities that these attacks are originating out of Russia.

"Let it be known that these criminal acts are greatly compromising the effort by the global anti-doping community to re-establish trust in Russia further to the outcomes of the Agency's independent McLaren Investigation Report."

Yuliya Stepanova, the whistleblower for WADA's Independent Commission that exposed widespread doping in Russian athletics, had her ADAMS password illegally obtained last month.