Five men were arrested at their homes across the U.K. following cyber attacks by an internet hacking group called Anonymous that has backed WikiLeaks. (Gary Hershorn/Reuters)

Five men have been arrested in connection with recent cyber attacks conducted by an internet hacking group that has backed WikiLeaks, British police said.

The five, aged from 15 to 26, were arrested Thursday at their homes across the U.K. for their alleged involvement in hacking several company websites, police reported.

The cyber attacks were carried out by an online group called Anonymous, police said.

The loose-knit group of activists previously claimed responsibility for attacking websites of companies that have severed links with WikiLeaks since it began publishing its massive trove of secret U.S. diplomatic cables in November.

MasterCard, Visa, Amazon and PayPal were among those targeted by the campaign of denial-of-service attacks launched in December. 

Such attacks flood websites with traffic, making them unavailable.

Visa, Mastercard and PayPal had started refusing to allow donations to WikiLeaks, and Amazon ousted WikiLeaks from its servers.

Thursday's raid was part of a police probe into Anonymous that is carried out together with law enforcement agencies in Europe and the U.S.

Meanwhile, a company asked by Visa to investigate WikiLeaks' finances found no proof the group's fundraising arm is breaking the law in its home base of Iceland, according to a document obtained by The Associated Press.

But Visa Europe Ltd. said Wednesday it would continue blocking donations to the secret-spilling site until it completes its own investigation. Company spokeswoman Amanda Kamin couldn't say when Visa's inquiry, now into its eighth week, would be finished.