A British student attacked the PayPal website in a hack which cost the site millions, a court has heard.
Northumberland University student Christopher Weatherhead, 22, allegedly took part in a campaign orchestrated by the Anonymous hacking collective.
The online payment site reportedly became a target of 'hacktivist' groups after it refused to process donations to online whistleblower WiikiLeaks.
Prosecutors told the court that the attack had cost PayPal £3.5 million (USD$5.5, AUD$5.3) and "caused considerable damage to its reputation and loss of trade."
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Mr Weatherhead pleaded not guilty to charges of conspiring to impair the operation of computers between August 1 2010 and January 22 2011.
Southwark Crown Court heard that Weatherhead, along with three other individuals who had already pleaded guilty to the charge, had turned its attentions to PayPal following a campaign against opponents of internet piracy.
Sandip Patel, prosecuting, told the court: "It is the prosecution case that Christopher Weatherhead, the defendant, is a cyber attacker and that he, 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, and those attacks caused unprecedented harm.
The court also heard how over 100 PayPal employees spent three weeks cleaning up the mess following the attacks and had spent £3.5m to protect the site against future attacks.
The case continues.