Image caption Christopher Weatherhead attacked the PayPal website

Two men who carried out cyber attacks for the Anonymous hacking group have been jailed.

Christopher Weatherhead, 22, of Northampton, and Ashley Rhodes, 28, of Camberwell, London, were jailed for 18 months and seven months respectively.

The two men carried out distributed denial of service, or DDoS, attacks which paralyse computer systems by flooding them with online requests.

The ones they attacked included payment site PayPal, costing it £3.5m.

Co-defendant Peter Gibson, of Hartlepool, was given a six-month sentence, suspended for two years.

Another defendant, Jake Birchall, 18, from Chester, will be sentenced on 1 February.

'You're being stung'

The sentences were handed down at Southwark Crown Court and are thought to be the first convictions for DDoS in the UK.

Weatherhead and Rhodes were found guilty of conspiring to impair the operation of computers between 1 August 2010 and 22 January 2011.

Gibson was deemed to have played a lesser role in the conspiracy and admitted his part, as did Birchall.

The websites targeted by the cyber attacks were chosen by Anonymous, as part of what it called Operation Payback, because the hackers did not agree with their views.

What is a DDoS attack? Attackers commonly use networks of compromised computers - called a botnet - that they control to launch the attacks

Hacking group Anonymous has recruited volunteers to download a tool to create a "virtual" botnet

By overwhelming the target site with requests, the attackers can ensure that genuine visitors cannot reach the site

These requests look like genuine web traffic so can be hard to filter out

Typically, such attacks have been aimed at high-profile websites, such as those belonging to government departments, banks and political organisations

They are illegal in most countries

Other companies hit by the attacks included Mastercard and Visa.

Southwark Crown Court had previously heard that PayPal was attacked after it decided not to process payments on behalf of the Wau Holland Foundation, an organisation involved in raising funds for the Wikileaks website.

Visitors to the affected websites in this case would 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."

Handing down his sentences, Judge Peter Testar said: "It is intolerable that when an individual or a group disagrees with a particular entity's activities, they should be free to curtail that activity by means of attacks such as those which took place in this case."

Prosecutor Joel Smith said theirs was a "persistent campaign" designed to "cause damage, financial losses and press exposure".

'Ideological twizzle'

The judge said the DDoS attacks had not been particularly sophisticated.

"What was sophisticated was the lengths taken to protect the identities of those involved," he said.

"The investigators are really to be commended for breaking down the wall of anonymity that was put up in order to prevent the activity of these conspirators being interrupted."

The Ministry of Sound estimated the cost of the attack on its sites as £9,000, while the International Federation of the Phonographic Industry's costs were more than £20,000 and the British Phonographic Industry's more than £4,000.

The financial impact on MasterCard and Visa were not revealed to the court, although Weatherhead once boasted online at having caused £1m worth of damage to MasterCard.

Gibson suggested attacking the website of singer Lily Allen, now known by her married name of Lily Cooper, as a possible target to Rhodes at one point. He agreed with the idea but the attack never went ahead.

Judge Testar told the court: "They got themselves into a bit of an ideological twizzle.

"On one hand, they wanted to attack her because she had taken a stand against breach of copyright. But on the other hand, they didn't like the idea of attacking artists."