Access to the website of Spain's national police force was blocked for over an hour late on Saturday in a reprisal attack by the hackers' group Anonymous, the newspaper El Mundo said on its website Sunday.
El Mundo said the group had warned police in a statement that it planned to disable the website at some time Saturday. The website was down for at least an hour from 2130 GMT, the paper said.
Spanish police arrested three suspected members of the group Friday on charges of cyber attacks against targets including the websites of Sony Corp, governments, businesses and banks -- but not the massive hacking of PlayStation gamers that Sony has reported in recent weeks.
Sunday, a spokesman for the police said access to the website www.policia.es had been blocked at 2 a.m. Sunday, 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.
In a statement cited in a later article in El Mundo, 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, El Mundo cited the statement as saying.
Anonymous is a loose grouping of activists lobbying for Internet freedom who frequently try to shut down the websites of businesses and other organizations that they oppose.
Members cripple websites by overwhelming them with traffic in what are commonly known as denial of service attacks.
The group has attacked Turkish government websites in a protest against Internet censorship.
In a separate development, the International Monetary Fund became the latest known target of a major cyber attack 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 organization to undermine its clout.
(Reporting by Judy MacInnes; Editing by Kevin Liffey)