Nearly two dozen athletes from six countries and in five sports who competed in the 2012 London Olympics have tested positive for banned substances after doping samples were rechecked.

The International Olympic Committee made the announcement Friday, stating that it had retested 265 samples. The news follows revelations last week that samples from 31 athletes in the 2008 Beijing Games had suspicious results out of 454 retests.

"All athletes found to have infringed the anti-doping rules will be banned from competing at the Olympic Games Rio 2016," the IOC said in a statement.

Why are we learning about this now? The IOC says its scientists have better testing techniques now than were available during the past two summer Olympics. So they've been going back and reanalyzing hundreds of samples collected during those prior games.

"These reanalyses show, once again, our determination in the fight against doping," IOC President Thomas Bach said in the statement. The IOC says it's especially been focusing on athletes who might compete in Rio. "We want to keep the dopers away from the Olympic Games in Rio de Janeiro."

Last week, Russian state media announced that 14 of the 31 athletes the IOC suspects of doping at the Beijing Games were from Russia.

That's the latest development in a scandal involving accusations of a massive state-sponsored doping operation in the country. The former head of the Russian anti-doping lab, Grigory Rodchenkov, disclosed details about "one of the most elaborate — and successful — doping ploys in sports history" in a New York Times story published earlier this month. Russian anti-doping experts allegedly worked hand in hand with members of the country's intelligence service to unseal supposedly tamperproof urine sample bottles and to replace the urine from athletes who were doping with clean urine samples.

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