The group of Russian hackers allegedly behind one of the worst cyber bank frauds of the last decade was unmasked on Thursday, with its leader indicted in America and the full scale of purported crimes revealed in remarkable detail.

The Moscow-based unit was identified as Evil Corp and dubbed “the world’s most harmful cyber crime group” as British and American officials revealed the results of an investigation into the group and its activities that has lasted a decade.

Maksim Yakubets, 32, was accused of being the group’s leader and was indicted over two separate hacking schemes. A $5 million reward was announced by the US State Department for any information that leads to his arrest.

Customers of nearly 300 organisations in 43 different countries have been targeted by the group, with financial losses in UK alone assessed to be worth hundreds of millions of pounds.

Evil Corp was accused of ruthlessly exploiting online vulnerabilities, tricking people into clicking on internet links that would install viruses, scanning for bank account details and then creating wires transfers to “money mules” working with the hackers.