Hacking group LulzSec has claimed responsibility for a distributed denial of service (DDoS) attack on the website of the UK’s Serious Organised Crime Agency (SOCA).

The attack prompted the agency to take down its website, a spokesperson told the BBC, to prevent interruptions to other websites hosted by the same service provider. It was unavailable for some hours last night, and has been accessible only intermittently this morning.

Yesterday, LulzSec launched a campaign that it calls ‘Anti Security’, urging hackers groups to "open fire on any government or agency that crosses their path". "Top priority is to steal and leak any classified government information, including email spools and documentation," the group said. "Prime targets are banks and other high-ranking establishments."

In the last few hours, a document has surfaced on the Internet which claims LulzSec has obtained the entire UK census data. Lockheed Martin, the US defense contract that conducted the UK census, was the victim of a cyber attack last month, although this may have been the inspiration for a plausible hoax.

In a statement, the Census Office said: "We are aware of the suggestion that census data has been accessed. We are working with our security advisers and contractors to establish whether there is any substance to this."