WASHINGTON: The FBI has served more than 40 search warrants throughout the US as part of an investigation into computer attacks on websites of businesses that stopped providing services to WikiLeaks last month.

The FBI statement announcing the search warrants was the first indication that the US intends to prosecute the so-called hacktivists for their actions in support of WikiLeaks.

The search warrants were executed on the same day authorities in Britain announced that they had arrested five people over the attacks, which temporarily crippled the websites of Amazon.com, PayPal, MasterCard, Visa, the Swiss bank PostFinance and others.

Law enforcement agencies in France, Germany and the Netherlands have also sought to find those involved with the attacks.

FBI officials were unavailable for comment, and the statement did not say who was served or where the searches were conducted. The statement said that attacks, known as distributed denial of service attacks and which use easily available software to shut down a computer network by flooding it with millions of requests for information, violate US law and are punishable by a prison sentence of 10 years.

The statement noted that a group known as Anonymous had claimed credit for the attacks. Anonymous is also believed responsible in recent days for attacks on government websites in Tunisia and Egypt.

British news reports said three of the five arrested were teenagers, aged 15, 16 and 19. Dutch police last month arrested two teenagers suspected of involvement in the online campaign.

The attacks were organised through social networking sites such as Twitter in the days after WikiLeaks began publishing US State Department cables that had allegedly been downloaded by a US Army private serving in Iraq. Their first target was Amazon.com, which, at the behest of a US senator, Joe Lieberman, had stopped hosting the WikiLeaks website.

They spread to PayPal, MasterCard and Visa after those businesses declined to process credit-card payments destined to WikiLeaks.

PostFinance, a bank operated by Switzerland's postal service, also closed an account that was registered to Julian Assange, the founder of WikiLeaks. The account number had been published on the WikiLeaks website with a solicitation for donations.

The attacks did no long-term damage and in most cases only lasted a few hours. But legitimate would-be users were unable to contact the sites while the attacks were under way.

The FBI said it was working with European governments and the National Cyber-Forensics and Training Alliance to identify the source of the attacks, which the FBI attributed to a type of software it identified as ''Low Orbit Ion Cannon'' tools. It said major anti-virus programs had been updated to block such software.

Previously, the only known criminal investigation stemming from WikiLeaks's publication of US State Department cables was one that seeks to tie Mr Assange to the army private Bradley Manning, who is suspected of providing the cables to the site.

Agencies