(Reuters) - Cyber activists attacking organizations seen as foes of WikiLeaks briefly blocked a Dutch prosecution website on Friday after a 16-year-old boy suspected of involvement in the campaign was arrested in the country.
The campaigners also tried to block the website of online payment firm Moneybookers, but denied their attacks were intended to create business turmoil or badly disrupt online Christmas shopping.
Several companies have ended services to WikiLeaks after it published thousands of secret U.S. diplomatic reports that have caused tension between Washington and several of its allies.
The website continued its release of U.S. cables on Friday, with the latest reports including a prediction by the U.S. ambassador to Cairo that Egyptian President Hosni Mubarak would "inevitably" win 2011 polls and stay in office for life.
The Dutch prosecution service said activists targeted its website with "denial of service" attacks that slowed it down for several hours in the morning and briefly made it unavailable, adding the incident was probably related to the boy's arrest.
"We have been investigating this with international authorities and we are working together with the FBI," Dutch prosecution service spokesman Wim de Bruin said, referring to the U.S. Federal Bureau of Investigation.
On Friday a Rotterdam judge ordered the boy, who was arrested in The Hague on Thursday in connection with the cyber attacks, to spend the next 13 days in custody while the investigation continues, the prosecution service said.
The suspect had told investigators he participated in the attacks on the websites of MasterCard and Visa. He is being held at a juvenile prison, De Bruin said, without offering more details about the boy's identity or background.
The attack on Moneybookers appeared to have frozen the site for about two minutes at about 1235 GMT but it subsequently came back online. The activists promised to continue their assault and spoke of MasterCard and Interpol as fresh targets.
Activists said Moneybookers had become a target because it had informed WikiLeaks in August it had closed its account.
Some participants in a chat room used by the so-called Operation Payback campaign voiced despair at what they saw at its lack of organization and discipline.
"The whole thing is getting out of control, people are attacking local police websites and giving us a bad reputation. This was supposed to be to help WikiLeaks and not an excuse for kids to crash random websites," one wrote.
Others were defiant. "If we don't panic, and we get bigger, no one can stop us," wrote a chat room participant.
In a statement, Moneybookers confirmed its website had been unavailable for a few minutes but the service was back up.
"We have been tightening security and applying additional vigilance which means that despite the attacks we continue to provide our service to users and merchants 24/7," it said.
The activists, who collectively call themselves Anonymous, said in a statement they were not hackers but rather "average Internet Citizens" whose actions were merely symbolic.
"We do not want to steal your personal information or credit card numbers. We also do not seek to attack critical infrastructure of companies such as MasterCard, Visa, PayPal or Amazon," the statement said.
Online retail and web-hosting powerhouse Amazon stopped hosting WikiLeaks' website last week, and on Thursday it briefly became the main target of the pro-WikiLeaks campaigners -- before they admitted it was too big for them, for the moment.
The Anonymous statement added that a lack of firepower was not the only reason the attack on Amazon had not succeeded. It felt "attacking a major online retailer when people are buying presents for their loved ones, would be in bad taste."
The Anonymous statement followed one by WikiLeaks which said the website had no links to the cyber attacks, and neither supported nor condemned them. The statement quoted WikiLeaks spokesman Kristinn Hrafnsson as saying the attacks were "a reflection of public opinion on the actions of the targets."
"Organize FOR SUCCESS"
Some freedom of information campaigners sympathetic to WikiLeaks look askance at the attacks, saying its cause cannot be furthered by denying freedom of information to others.
On an online chat service used by the campaign, participants debated whether to end the attacks and focus instead on discovering more embarrassing material in the leaked documents.
Another statement purportedly from Anonymous organizers called on activists to stop attacking for the moment and await instructions. "We have to organize for success," it said.
(Additional reporting by Georgina Prodhan in London, Marius Bosch in Johannesburg and Greg Roumeliotis in Amsterdam)
(Writing by William Maclean; editing by David Stamp)