The Football Association and Fifa have condemned the latest hack by the Fancy Bears group after details of failed drug tests and therapeutic use exemptions (TUEs) among footballers were made public.

A small cache of emails between Fifa staff and doping officials were leaked by the Russian hacking group on Tuesday. Alongside the correspondence, which has not been verified by the Guardian, Fancy Bears claimed that 25 players had been allowed to use TUEs at the 2010 World Cup, including the former Premier League players Dirk Kuyt, Juan Sebastián Verón and Carlos Tevez.

Tevez, his Argentina team-mate Verón and Holland’s Kuyt were apparently prescribed corticosteroids, a class of steroid hormone. These TUEs are legal under World Anti-Doping Agency (Wada) rules and there is no suggestion that any of the players have done anything wrong.

In a statement the FA said it was disappointed at the information having been made public, after the leak included conversations between the FA’s head of integrity, Jenni Kennedy, and colleagues at Fifa.

Fancy Bears further claimed that 150 players had failed drug tests in 2015, including four in the UK where three tested positive for cocaine and one for ecstasy. Information regarding two ongoing doping investigations by the FA is also believed to have been leaked.

“The Football Association is disappointed that strictly confidential information has been released into the public domain,” the FA said in a statement. “The details of ongoing cases cannot be discussed or disclosed until due legal process has been completed.

“Additionally, it is inappropriate to publish information relating to personal medical conditions or medications and we will work alongside our partners to ascertain the extent of this matter.”

Fifa was strident in its criticism of the leaks. “Fifa condemns in the strongest terms the publication by the Fancy Bears group of information obtained illegally, particularly personal and medical data from athletes.

“The release of such information constitutes a clear violation of the athletes’ privacy and puts at risk the ongoing fight against doping.”

This is the first time the Fancy Bears group has released information about footballers. The group, which is believed to be acting as an extension of the Russian intelligence agencies, first came into public prominence last year after revealing a tranche of medical records stolen from the Wada database.

Three key questions

What is a TUE?

It is an exemption that allows an athlete to use medication that is on Wada’s prohibited substances list because of an illness or condition.

What is the issue with TUEs?

Some believe that athletes are granted TUEs when they are not needed, allowing them an edge in performance. Dr Ross Tucker, an exercise physiologist and high-performance sports science consultant, points to the high use of corticosteroids, which are given to athletes to help them breathe better yet can also be performance-enhancing.

How can we be sure that TUEs are being assessed accurately?

In theory an athlete should get a TUE only after an independent committee – which, according to Wada, should have at least three sports medicine physicians on it – has met and made a recommendation to a sporting body or a national anti-doping organisation, which then either approves or refuses the request. When making their ruling, the doctors must take into account a number of factors – including the need to protect a competitor’s health, ensure a substance is not performance-enhancing and that there is no other reasonable non-banned alternative. Sean Ingle