The Southwark Crown Court in London has heard that four hackers from the `Anonymous' hacking group avenged the backlash against WikiLeaks by launching cyber-attacks which caused a £3.5 million ($5.4 million) loss to PayPal, and multimillion-pound losses to several other firms.

The court was told that the four self-styled Anonymous `hactivists' carried out a series of cyber attacks using the name `Operation Payback'; and virtually inundated the websites belonging to a number of companies - including PayPal and Ministry of Sound - with messages and requests, with the aim of making them go offline.

Three of the Anonymous hackers involved in `Operation Payback' - which cost PayPal over £3.5 million, and brought down the websites of MasterCard and the recording industry - have admitted to their role in the cyber-attacks.

The fourth accomplice - a 22-year-old Northampton University student named Christopher Weatherhead - is currently on trial at Southwark Crown Court; and faces the allegation that he was "part of a small cabal of leaders" of the cyber-attacks carried out between August 1, 2010 and January 22, 2011.

Opening the prosecution case at the London court, Sandip Patel said that Weatherhead - known by the online name `Nerdo' - played a key role in the `Operation Payback' cyberattacks; and added: "He (Weatherhead) and others like him waged a sophisticated and orchestrated campaign of online attacks that paralysed a series of targeted computer systems belonging to companies, to which they took issue with for whatever reason, that caused unprecedented harm."