The Serious Organised Crime Agency (Soca) website has been taken temporarily offline after a distributed denial of service attack by computer hackers, a spokesman said today.
The distributed denial of service (DDoS) attack - which involves web addresses being hit by a flood of visits - was carried out last night, a Soca spokesman said.
The incident did "not pose any security risk to the organisation", he added.
The attack comes after the Number 10 and Home Office websites were brought down by DDoS attacks in the past months.
DDoS attacks on the Soca website have previously been linked to the loose-knit international "hacktivist" group Anonymous.
Soca's website has been down since 10pm last night.
A spokesman said: "The action was taken to limit the impact of a DDoS attack on other clients hosted by our service provider.
"Soca's website contains only publicly available information and does not provide access to operational material."
Soca said the attack was not of any operational threat.
This is the second time that hackers have targeted Soca. Last June, the former hacking group Lulz Security launched a similar DDoS attack on the website.