A student committed a series of cyber attacks as part of hacking group Anonymous that cost the website PayPal £3.5 million, a court heard today.

Christopher Weatherhead, 22, was studying at Northampton University when he is alleged to have taken part in the cyber campaign which also attacked other sites including MasterCard, Visa, Ministry of Sound, the British Recorded Music Industry (BPI) and the International Federation of the Phonographic Industry (IFPI).

London's Southwark Crown Court heard the group initially targeted companies involved in the music industry and opponents of internet piracy, costing them thousands of pounds, but then broadened their attack to companies such as PayPal after it refused to process payments on behalf of WikiLeaks.

Opening the case, prosecutor Sandip Patel said the group caused online payment processing site PayPal "enormous economic harm".

He said it was attacked after it decided not to process payments on behalf of the Wau Holland Foundation, an organisation involved in raising funds for WikiLeaks.

Three days later, on December 6 2010, Weatherhead posted plans on an Internet Relay Chat (IRC) channel encouraging an attack on the online payments processing website.

He suggested they should "reap", thought to mean "rape", PayPal, the court heard.

Mr Patel said the defendant devised a plan to make it look as though PayPal was attacking internet service providers (ISPs), which would make it impossible to prove that they had initiated the attack.

An online conversation between Weatherhead, who went by the online name of Nerdo, and someone called Neo said: "I think we should do something really bad, give spoofed IPs of PayPal etc, and get ISPs, it would be awesome, you know it's true."

Between December 8 and 17 2010, PayPal was the victim of a series of attacks "which caused considerable damage to its reputation and loss of trade".

At least 104 employees from eBay, the parent company of PayPal, were employed to work on issues directly related to the attack for three weeks afterwards, the court heard.

PayPal also had to pay for further software and hardware to defend against similar future attacks.

Mr Patel said that this, combined with the loss of trading, led to the £3.5 million loss.

The case showed the "dark side" of the internet and the group's attacks were "split into organised and co-ordinated attacks almost along military lines", he added.

Weatherhead, of Holly Road, Northampton, denies a charge of conspiracy to impair the operation of computers between August 1 2010 and January 22 last year.

Jurors were told that three other men have already pleaded guilty to the charrge.

The amount the hacking cost MasterCard and Visa was not given but the court heard that the defendant, in an IRC conversation with someone called Tred, boasted: "We have probably done some million pound of dmg (damage) to mc (MasterCard)."

The BPI was the subject of an attack on September 19 and 20 2010, leading it to have to pay out £3,996 for online security in the aftermath, plus hundreds of pounds in other costs.

The four websites run by the Ministry of Sound were targeted in two separate attacks between October 2 and 6 2010, which cost the company around £9,000 in additional staffing, software and loss of sales.

And the financial cost to the IFPI was more than £20,000 as its website was down for nine days when it was hacked between November 27 and December 6 2010.

Mr Patel said members of Anonymous were self-styled "hacktivists" who believe that everything on the internet should be free with no copyright protection.

Their attacks, codenamed Operation Payback, began as a campaign against the music industry and those involved in anti-piracy measures following legal proceedings against the Pirate Bay website which had attempted to distribute music in breach of copyright laws.

Its members used online chat services to discuss, plan and co-ordinate their attacks, primarily using Internet Relay Chat.

After deciding what websites to target, they carried out distributed denial of service, or DDoS, attacks, which meant they paralysed a computer system by flooding it with an intolerable number of online requests.

Victims of attacks would find their website would suddenly crash and be directed to a page displaying the message: "You've tried to bite the Anonymous hand.

"You angered the hive and now you are being stung."

Not all the organisations that were hacked contacted police, and many would have had no idea what was happening to their website, the court heard.

Mr Patel said: "This case, simply put, is about hackers who used the internet to attack and disable computer systems - colloquially described as cyber attackers or vandals.

"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."

Mr Patel said Weatherhead "played a central and integral role in the overall effectiveness" of the cyber campaign.

He told jurors: "It does not matter at what stage a person joins a conspiracy. All the prosecution must make you sure of is that the defendant at some stage in the course of the conspiracy agreed with one or the other conspirators to commit the crime in question."

The case continues.