[Photo:  At Festival of Economics, 2012  -  by Niccolo Carati / Wikimedia Commons]

The Dutch market regulator mistakenly published the details of hundreds of private short sales trades going back to 2012 by international hedge funds - including George Soros and Renaissance Technologies' enigmatic Medallion fund. An error by the AFM, the Netherlands' watchdog, meant that details of hedge fund short trades going back to 2012 were published on its website on Tuesday evening before being quickly removed.

European market rules introduced after the financial crisis require hedge funds to report their short positions to regulators. The regulator instead published details of all short trades reported in the Netherlands since the new rules came into force, meaning hundreds of previously non-public trades were briefly released into the public domain.

Hedge funds whose trades were included in the release were angry. "When a bank or hedge fund makes a mistake they are fined - who will fine the Dutch regulator?" asked one manager.

A list of the trades seen by the Financial Times included a number of previously unreported short positions including George Soros' family office betting against the Dutch bank ING, a trade that chimes with its existing public bet against Germany's Deutsche Bank. The position against ING was opened in June and was increased to as much as 0.3% of the lender's shares before being scaled back a month later.

Other previously private trades in the list include bets by the computer-driven Medallion fund operated by the US hedge fund Renaissance Technologies. The fund, which was launched in the early 1980s by mathematician and code breaker James Simons, has long been closed to outside investors and only manages the fortunes of the Renaissance partners.