The online cyber war being waged against companies that have refused to host WikiLeaks or process donations to the whistle-blowing website intensified |dramatically yesterday.

In a vivid illustration of the nature of the internet, websites perceived to be anti-WikiLeaks were struck by attacks — among them Amazon, Paypal, Sarah Palin, the US State Department and the Swedish government.

The renewed cyber assaults by members of the hacker group Anonymous came after the disruption on Wednesday of payment systems for Visa and Mastercard, both of which declined to process donations to WikiLeaks.

Anonymous, a shadowy and highly decentralised collective of cyber activists who vote on who to target through message boards, |recruited an army of volunteers to attack websites that have recently disassociated themselves from WikiLeaks in an action called |Operation Payback.

By last night, 31,000 people had downloaded special software |allowing them to target their |perceived opponents with distributed denial of service attacks (DDoS), a relatively simple way of slowing down or temporarily closing a website by flooding it with requests for information. The software allows computers to join a botnet — a large collection of machines that use their combined power to target one site at a time.

Usually DDoS attacks are launched by computers hijacked by a virus or malicious code, but the Anonymous botnet, which |activists call a “low orbit ion-|cannon” in a geeky nod to sci-fi films, is a voluntary network.

Knowingly taking part in a DdoS attack is illegal in the UK and could land users with a two-year jail sentence.

The renewed attacks came as WikiLeaks yesterday released its first comments on Anonymous.

“We neither condemn nor applaud these attacks,” said WikiLeaks spokesperson Kristinn Hrafnsson. “We believe they are a reflection of public opinion on the actions of the targets.” A statement added: “[Anonymous] group is not affiliated with WikiLeaks.”

Hours before, the UN's top human rights official criticised websites that have refused to host WikiLeaks, suggesting it breached the platform's right to freedom of expression.

High Commissioner for Human Rights, Navi Pillay, told reporters that the moves “could be interpreted as an attempt to censor the publication of information”.

Following the Anonymous attacks, there have been reprisal attacks on websites popular with hacktivist networks. Such attacks are thought to be the work of “freelance patriot” American hackers that first attacked Wikileaks two weeks ago.