By Max Clarke

A coalition of anonymous hackers who identify themselves as 'Operation Payback' have launched a series of online attacks against companies deemed opposed to Wikileaks' founder Julian Assange.

Operation Payback began life as a 'hacktivist' attack directed against online piracy, with torrent host website thepiratebay.org becoming a major target.

As an act of solidarity towards Julian Assange, the founder of the whistle blowing website WikiLeaks, the loose coalition of online hackers yesterday directed their attacks on opponents of Mr. Assange and his site, including the Swedish Prosecution Authority, PostFinance, and PayPal.

The Mastercard and Visa websites were successfully brought to their knees, for allegedly bowing to pressure from the US government and ceasing business with WikiLeaks. Mastercard’s site is once again up and running, though its homepage acknowledges it has suffered “limited interruption in some web-based services“.

Speaking to the BBC, one hacker, identified only by the alias Coldblood, defended the group's actions by stating "We are trying to keep the internet open and free but, in recent years, governments have been trying to limit the freedom we have on the internet."

Social networking giants Twitter and Facebook have removed the group's pages, who coordinate their actions via the 4chan imageboard website.