Russian cyber spies recently hacked the World Anti-Doping Agency and stole the medical data of international Rio 2016 Olympic athletes.

The hackers—known as Tsar Team or Fancy Bear—gained access to WADA's Anti-Doping Administration and Management System database, likely via a phishing email, according to WADA. Some details—including files on gymnast Simone Biles, basketball star Elena Delle Donne, and tennis pros Serena and Venus Williams—have already been leaked to the public.

pic.twitter.com/tPxCJ1K2RZ — Simone Biles (@Simone_Biles) September 13, 2016

"We'll keep on telling the world about doping in elite sports," the Fancy Bear website says. "Stay tuned for new leaks."

"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," Director General Olivier Niggli said in a statement. "[We] condemn these ongoing cyber-attacks that are being carried out in an attempt to undermine WADA and the global anti-doping system."

It appears the hackers were only after info about the Summer Games; no other data has been compromised, according to the agency, which is conducting internal and external security vulnerability checks.

The attack comes only a month after Yuliya Stepanova's WADA database password was stolen and her account illegally accessed. Stepanova was the key whistleblower who helped expose widespread doping among Russian athletes. The country's track and field team was ultimately banned from the Rio Olympics, and all athletes were barred from the Paralympics.

"Let it be know 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," Niggli said.

Fancy Bear was linked to the hack of the Democratic National Committee this summer. Crowdstrike co-founder Dmitri Alperovitch said at the time that Fancy Bear has targeted defense organizations around the world, suggesting they are aligned with GRU, Russia's military intelligence service.