'Anonymous' Calls It War After US, UK Police Go After Hackers

International law enforcement is on a mission, hacktivists say: They're out to pay back the anonymous hackers who were part of last year's "Operation Payback," most notably in support of WikiLeaks.

Police arrested five young men in Britain on Thursday, and more than 40 search warrants were executed by the FBI. Police in France, Germany and the Netherlands are also part of the effort.

The targets are those who go by the name of "Anonymous," a loosely organized band of international hackers best known for briefly shutting down some big corporate websites late last year that had cut ties with WikiLeaks.

Anonymous, in turn, called the crackdown a "sad mistake" in a statement issued after the arrests, which it called an "act of war."

"You can easily arrest individuals, but you cannot arrest an ideology. We are united by a common objective, and we can and will cross any borders to achieve that," Anonymous said. "So our advice to you, the U.K. government, is to take this statement as a serious warning from the citizens of the world. We will not rest until our fellow anon protesters have been released."

The FBI said that the attacks were carried out with the aid of software the group made available for free on the Internet.

"The FBI is working closely with its international law enforcement partners and others to mitigate these threats," the FBI said in a statement.

A team of London detectives who specialize in cybercrime detained the five young men, ages 15 to 26, in raids at homes in central and southern England, Reuters reported.

Among them was reportedly Coldblood, a young Internet activist who says he does not work with Anonymous but explained how the group works in many TV appearances last December.

A source close to Coldblood told AOL News that his TV appearances had angered someone in Anonymous, who then used the name "Coldblood" when participating in cyber-attacks. Police then arrested the real Coldblood in connection with those attacks, the source said.

An Internet activist with knowledge of the anonymous-hacker underground told AOL News today that police are using "old, old techniques" that are unlikely to make a dent in the more than 10,000 strong Anonymous community, despite the arrests in Britain.

"So they got a few people and some servers," said Boston-based Gregg Housh. "Everything was back to normal after the raids."

Anonymous is also responsible for attacking Tunisian websites this month and has encouraged people to download its "Operation Egypt" software aimed at protesting the Internet shutdown in Egypt today.

In December, sites belonging to PayPal, Visa, MasterCard and Amazon.com were targeted in the distributed denial of service (DDoS) attacks at the end of December. It was thought that the raids carried out Thursday were in response to those attacks.

DDoS attacks involve swamping a site's server with so many requests that it temporarily goes down.

But Housh, who spoke to three hackers whose homes were raided by police Thursday, said they were all questioned about music industry sites, not the sites involving WikiLeaks.

What many people don't know, Housh told AOL News, is that Operation Payback began six months ago and first targeted the music industry because of court cases against people for file-sharing.

Anonymous has reportedly grown exponentially since just the end of December, The Guardian reported today.

The group is believed to have grown significantly in number and firepower since its support of WikiLeaks, with the overwhelming majority of users simply volunteering their computer to be used in the attacks. Most of those involved in Anonymous operations do not disguise their Internet protocol address, meaning they can be easily identified by police.