The Russian hacker group allegedly responsible for leaking Serena and Venus Williams' World Anti-Doping Agency (WADA) records has also released Petra Kvitova and Bethanie Mattek-Sands's records. All  have shown that they have had therapeutic use exemptions (TUEs) approved.

The Williams sisters were among the 29 athletes whose records were released in the first round of leaks.

Kvitova has asthma and received TUEs for albuterol and formoterol (both used for asthma treatment) starting in 2009. Mattek-Sands received TUEs for hydrocortisone, and also initially for DHEA, a banned anabolic agent. The DHEA was subsequently revoked by WADA.

The ITF's Stuart Miller, who runs the anti-doping program, told the New York Times that about 100 requests for TUEs are filed each year in tennis, including some which are subsequently withdrawn. He said that each is assessed by a medical panel that does not know the identity of the athlete and about 50-60 percent are approved. WADA can also question and deny approvals.

Miller added that the Mattek-Sands request for DHEA that was made in 2013 is the only time a TUE has been approved by the ITF and then turned down by WADA since the ITF began running the program. The American appealed to the Court of Arbitration for Sport and was also rejected.

The New York Times also questioned the background of Mattek-Sands's doctor, who appears to have previously advocated the use of banned substances.

A spokesperson for Kvitova and the Czech tennis federation, Karel Tejkal said it was "no secret" that the two-time Grand Slam champion has asthma and that is was "ridiculous and reprehensible" for the release of confidential records.

WADA's director general called the attack on its system "retaliation" for the agency's investigation into a state-sponsored Russian doping system. The Russian government has denied any involvement.

WADA also said that none of the athletes affected have been shown to have committed a doping violation.