FBI agents executed more than 40 search warrants on Thursday as part of an investigation into coordinated web attacks carried out by the hacking collective known as Anonymous.

The distributed denial-of-service attacks targeted US companies that angered the ragtag group, presumably because they cut off services WikiLeaks needed to raise money. The search warrants coincided with the early morning arrests of five UK youths accused of participating in the DDoS spree.

Word of the crackdown first surfaced in the US four weeks ago. Metropolitan Police in the UK confirmed their investigation in mid December.

Anonymous members have said the assaults were in retaliation for attempts to stifle the secret-spilling website. Group members on Thursday stepped up the bluster with a press release declaring war on UK authorities for having the nerve to enforce their country's laws.

The FBI was undeterred.

“The FBI also is reminding the public that facilitating or conducting a DDoS attack is illegal, punishable by up to 10 years in prison, as well as exposing participants to significant civil liability,” the agency said in a press release.

Thursday's arrests were part of an international police probe carried out by law enforcement agencies throughout Europe and the US. A French official told the Associated Press that a 15-year-old suspected of masterminding the attacks was arrested in December. The unidentified teen has since been released, but his computer was confiscated.

That same month, a 16-year-old boy in the Netherlands was arrested for allegedly carrying out attacks on Visa and MasterCard after the credit card companies stopped processing payments to WikiLeaks.

Researchers have said members of Anonymous modified a piece of open-source software to create what they call the Low Orbit Ion Cannon. The tool allows large groups of online protestors to simultaneously unleash torrents of data on websites they want to bring down. While it's relatively effective, it does nothing to cloak the IP address of those who use it, making it easy for investigators to catch those participating in the attacks. ®