The Fancy Bears hacking group has released a number of documents it claims show US sports officials "covering up" doping activity.
The group has gained notoriety since publishing confidential medical data belonging to athletes who competed at the 2016 Olympic Games, including Serena Williams, Mo Farah and Bradley Wiggins.
Data released was in relation to Therapeutic Use Exemptions (TUEs) - the means by which an athlete can obtain approval to use a prescribed prohibited substance or method for the treatment of a legitimate medical condition.
Leaked information - lifted from the World Anti-Doping Agency's (WADA) ADAMS system - was published in six parts over the course of a week, but WADA questioned the validity of some of the data made public by Fancy Bears.
A WADA statement on Wednesday read: "It should be noted that in the course of its investigation, WADA has determined that not all data released by Fancy Bear [in its PDF documents] accurately reflects ADAMS data.
"However, we are continuing to examine the extent of this as a priority and we would encourage any affected parties to contact WADA should they become aware of any inaccuracies in the data that has been released."
Fancy Bears has responded by signalling its intention to launch another sustained series of leaks, beginning with a collection of e-mails it says were sent by US officials, including some at the United States Anti-Doping Agency (USADA), revealing further data relating to TUEs.
"We've got a few e-mails of the US sports officials who are involved in covering up doping," reads the introduction to the release.