Internet activists defied efforts to end their online assaults against institutions seen as enemies of WikiLeaks today, promising more cyber attacks on targets starting with PayPal.
The campaign to avenge WikiLeaks against those who have obstructed its operations, calling itself Operation Payback, has already temporarily brought down the websites of credit-card giants Visa and MasterCard, and of the Swedish government.
A succession of US institutions has withdrawn services from WikiLeaks after the website published thousands of sometimes embarrassing secret US diplomatic reports that have caused strains between Washington and several allies.
Online retail and web-hosting powerhouse Amazon last week stopped hosting WikiLeaks' website, and today it briefly became the main target of the pro-WikiLeaks campaigners -before they admitted it was too big for them, for the moment.
"We cannot attack Amazon, currently. The previous schedule was to do so, but we don't have enough forces," read one message on Twitter.
The activists said they would instead attack PayPal, which has suspended the WikiLeaks account that the organisation had used to collect donations. MasterCard and Visa had also become targets after stopping processing donations.
This evening, the websites of PayPal, Amazon - a key Christmas shopping destination - MasterCard and Visa all appeared to be functioning normally.
Facebook said it had removed the activists' Operation Payback page today because it was promoting a distributed denial of service attack - a form of freezing websites by bombarding them with requests that is illegal in many countries.
The campaign also disappeared briefly from Twitter before reappearing in a different guise. Twitter declined to comment.
In an online letter, Anonymous, a loose-knit group, said its activists were neither vigilantes nor terrorists. It added: "The goal is simple: Win the right to keep the Internet free of any control from any entity, corporation, or government."
Some of the motivation for the cyber campaign appears to stem from anger at the arrest in Britain of WikiLeaks founder Julian Assange over alleged sex crimes committed in Sweden. He is in jail in London, awaiting an extradition hearing.
Mr Assange said last week he had expected clampdowns in countries such as the United States that championed free speech, and had deliberately picked providers like Amazon to host its data to test that theory.
In Moscow, Russian prime minister Vladimir Putin said the arrest of Mr Assange showed the West was hypocritical in its criticism of Russia's record on democracy.
When asked about leaked US diplomatic cables which cast him as Russia's "alpha-dog" ruler of a corrupt bureaucracy, Mr Putin questioned whether the US foreign service was a "crystal clean source of information".
UN High Commissioner for Human Rights Navi Pillay voiced concern today at reports of pressure being exerted on private companies to halt financial or internet services for WikiLeaks.
The campaign is not over from what I've seen, it's still going strong. More people are joining," a spokesman for the pro-WikiLeaks campaign Anonymous calling himself "Coldblood" told BBC Radio 4.
The speaker, who had an English accent, said he was aged 22 and was a software engineer.
"Anonymous has targeted mainly companies which have decided for whatever reason not to deal with WikiLeaks. Some of the main targets involve Amazon, MasterCard, Visa and PayPal."
In a statement today, MasterCard said although there was a limited interruption of some online services, cardholders could continue using cards for transactions worldwide. Its main processing systems were not compromised, the statement said.
The campaigners also claimed responsibility for bringing down Visa Inc's site, which was temporarily unavailable in the United States, but later restored. Swedish newspaper Aftonbladet said the Swedish government's website was down for a short time overnight in the latest apparent attack.
Mr Assange, a 39-year-old Australian, has been hailed as an advocate of free speech by supporters, but now finds himself fighting serious sexual allegations made by two women in Sweden.
Mr Assange will have another court appearance next Tuesday and his supporters assert he is being victimised for his work.
In the Internet Relay chat channel where activists coordinated the attacks, conversations were short and to the point. Participants asked what the target should be and reported progress. Some bemoaned the fact that PayPal's site remained up despite efforts to bring down its transactions server.
"The only thing most of these CEOs understand is the bottom line. You have to hit them in the bank account, or not at all," said one participant called Cancer.
WikiLeaks is continuing to drip-feed cables into the public domain despite the legal woes of its founder.
Those released today showed US diplomats reporting that the illicit diamond trade in Zimbabwe had led to the murder of thousands, enriched those close to president Robert Mugabe and had been financed in part by the central bank.
Mr Assange's main London lawyer has denied that the WikiLeaks founder ordered the attacks.
Reuters