Access to the website of Spain's national police force was blocked for over an hour late on Saturday in an apparent reprisal attack by the hackers' group Anonymous.
The El Mundo newspaper said the group had warned police in a statement that it planned to disable the website at some time on Saturday. The website was down for at least an hour that night.
Spanish police arrested three suspected members of the group on Friday on charges of cyber attacks against targets including the websites of Sony Corp, governments, businesses and banks.
A spokesman for the police said access to the website had been blocked, but that the cause had not yet been established. "A website can collapse if too many people try to access it at once. I cannot confirm the link with the Anonymous group," the spokesman said.
However, a statement was posted on a website linked to Anonymous claiming responsibility for the hack, which it called #OpPolicia. Anonymous denied that the three arrested suspects were a 'core group', as stated by the police. "They did not arrest any core group ... because we don't have a core group," the statement said.
Anonymous is a loose grouping of activists lobbying for internet freedom who frequently try to shut down the websites of businesses and other organisations that they oppose. Members cripple websites by overwhelming them with traffic in what are commonly known as "denial of service" attacks.
The Fine Gael website was the subject of a cyberattack claimed by someone purporting to be from Anonymous last January. The group has also attacked Turkish government websites in a protest against internet censorship.
The International Monetary Fund became the latest known target of a major cyberattack on Saturday.
Jeff Moss, a self-described computer hacker and member of the Department of Homeland Security Advisory Committee, said he believed that attack had been conducted on behalf of a country trying to either steal sensitive information about key IMF strategies or embarrass the organisation to undermine its clout.
Reuters