The World Anti-Doping Agency (Wada) has condemned Russian hackers for leaking confidential medical files of US Olympic athletes.
Athletes affected include tennis player Serena Williams and gymnast Simone Biles.
A hacking group calling itself "Fancy Bears" claimed responsibility.
Wada said the cyber attacks were an attempt to undermine the global anti-doping system.
Russia's track and field team were banned from the Rio Olympics over an alleged state-backed doping programme.