The Greek government and its international creditors began work on a mammoth new bailout on Monday overshadowed by revelations that Greece's former finance minister had been secretly planning for a parallel system of liquidity.

As the European Commission confirmed that technical talks on Greece's third bailout had started in Athens, the embattled leftist government was put on the defensive by Yanis Varoufakis' claim that his own ministry was "hacked" weeks earlier to create duplicate files for millions of Greek taxpayers.

In a telephone conversation with a group of London-based investors after he resigned his post on July 6, Varoufakis claimed that Prime Minister Alexis Tsipras had "given the green light" for a secondary plan before coming to power in January, according to a recording released on Monday.