Two computer hackers have been jailed by a London court for a series of cyber-attacks by Anonymous that cost online giant PayPal millions of dollars.

Christopher Weatherhead, 22, was found guilty last month of carrying out attacks on PayPal, MasterCard, Visa and other companies that refused to process payments to whistleblowing website WikiLeaks.

Ashley Rhodes, 28, admitted the same charge of conspiring to impair the operation of computers between August 1, 2010 and January 22, 2011.

Weatherhead has been sentenced to 18 months in jail, while Rhodes has been jailed for seven months.

Another hacker, 24-year-old Peter Gibson, had also pleaded guilty but was deemed to have played a lesser role in the attacks and was given a six-month suspended sentence.

A fourth man, 18-year-old Jake Birchall, who also admitted his involvement, will be sentenced later.

PayPal was repeatedly attacked in December 2010 after the website decided not to process payments made to the Wau Holland Foundation, an organisation involved in raising funds for Julian Assange's website WikiLeaks.

During Weatherhead's trial, prosecutors said the attack had cost PayPal $5.5 million in loss of trading as well as software and hardware updates to fend off similar attacks.

The so-called distributed denial of service (DDoS) attacks paralyse computer systems by overloading them with online requests.

Targeted websites were directed to a page reading: "You've tried to bite the Anonymous hand. You angered the hive and now you are being stung."

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 trial had heard.

AFP