A British student went on trial in London on Thursday accused of a series of cyber-attacks by the hacking group Anonymous that cost the US online payments giant PayPal millions of dollars.
Christopher Weatherhead, 22, is accused of participating in attacks by Anonymous on PayPal, MasterCard and other companies that refused to process payments to the whistleblowing website WikiLeaks.
Prosecutors said the assault on PayPal had cost the company £3.5 million ($5.6 million, 4.3 million euros) in loss of trading as well as software and hardware updates to fend off similar attacks.
In a campaign codenamed "Operation Payback", Anonymous also targeted companies in the music industry and opponents of music piracy including the Ministry of Sound nightclub and record label, the jury heard.
Weatherhead denies a charge of conspiracy to impair the operation of computers between August 2010 and January 22 last year, when he was a student at Northampton University in central England.
Opening the case, prosecutor Sandip Patel said Weatherhead and other Anonymous members had "waged a sophisticated and orchestrated campaign of online attacks that paralysed a series of targeted computer systems".
"Those attacks caused unprecedented harm," Patel added.
Three other men have already pleaded guilty to the charge, the jury heard.
Anonymous, who style themselves as "hactivists", said on Saturday that they had downed dozens of Israeli government websites in protest over the Jewish state's air assault on Gaza, which ended with a wary truce on Wednesday.
Explore further: Hackers train sights on Yemen after Egypt