(AFP) - "Secret files" leaked to website Buzzfeed News and the BBC have alleged widespread match-fixing and corruption in tennis.

Below is a summary of the main allegations:

Tennis governing bodies were aware of a core group of 16 players in world's top 50 involved in match-fixing. None have been sanctioned.

Eight of the 16 are playing in the Australian Open, the season's first Grand Slam, which began on Monday.

One top-50 player currently in the Australian Open is suspected of repeatedly fixing his first set in matches.

Match-fixing is orchestrated by gambling syndicates in Russia and Italy who contact players in hotel rooms and offer $50,000 (S$71,900) or more.

The names of more than 70 players have appeared on nine leaked lists of suspected fixers, which were given to tennis governing bodies in the past 10 years.

After a 2008 probe, which implicated 28 tour players, all were allowed to continue playing without sanction.

Tennis Integrity Unit, which was set up to ensure fair play, admitted shelving the evidence of the 2008 report because a new integrity code they introduced afterwards "could not be enforced retrospectively".

The 2008 investigation was triggered by a notorious match between the world No. 4, Russia's Nikolay Davydenko, and Argentina's 87th-ranked Martin Vassallo Arguello, which attracted millions of dollars in highly suspicious betting on long-odds underdog Arguello to win from accounts originating in Moscow.

Davydenko was a set and a break up and cruising to victory when he pulled out injured. An investigation "was unable to find evidence" that either player had been involved in any corrupt practice.