The latest report from WADA stated that the full extent of the doping "will probably never be established"
The Russian Olympic team corrupted the London 2012 Games on an "unprecedented scale", an independent investigation has found.
Professor Richard McLaren, author of a report funded by the World Anti-Doping Agency, said: "The Russian Olympic team corrupted the London Games on an unprecedented scale, the full extent of which will probably never be established.
"The desire to win medals superseded their collective moral and ethical compass and Olympic values of fair play."
His investigation has found more than 1,000 Russian athletes have benefited from a systematic, state-sponsored doping cover-up across 30 sports.
These athletes include 78 whose positive tests were covered up in London Games, the report said. Fifteen of them were medallists at the Games.
No Russian athlete tested positive for a prohibited substance at the time.
"The [Russian] ministry of sport was working to discipline athletes in advance of the London Games into taking the cocktail of steroids ... in order to beat the detection thresholds at the London lab," Prof McLaren said at a news conference in London.
He said the state-sponsored corruption involved "the ongoing use of prohibited substances, washout testing and false reporting".
As well as at the London Games, the investigation found positive tests were covered up at Sochi 2014 and the 2013 World Athletics Championships.
Prof McLaren, a Canadian sports lawyer, said: "We are now able to confirm a cover-up that dates back until at least 2011 and continued after the Sochi Olympic Games.
"It was a cover-up that evolved from uncontrolled chaos to an institutionalised and disciplined medal-winning conspiracy."
He said the Russians had "hijacked" international sports competitions "for years".
"Sports fans and spectators have been deceived and it is time that this stops," he said.
UK Anti-Doping chief executive Nicole Sapstead said Prof McLaren's report was "hugely significant" and highlight how "anti-doping is woefully underfunded".
"WADA needs support and the ability to apply the right sanctions so that this type of situation cannot happen again," it said.