Under the campaign, which was branded “#OpFreeAssange,” Anonymous undertook a mission to take down justice.gov.uk and number10.gov.uk, the official site of the British Prime Minister’s Office. The websites are now operating normally once again.

Several Twitter accounts associated with the loose-knit Anonymous collective have acknowledged that the UK Ministry of Justice and the PM Office's websites had been targeted with a distributed denial-of-service, or DDoS, attack.

“#OpFreeAssange: TANGO DOWN! http://www.justice.gov.uk/ [500 Internal Server Error] [#Anonymous #WikiLeaks],” reads one tweet sent from the @Anon_Central Twitter account.

The hackers also claim to have taken down the website of another British government department – the Department of Work and Pensions. “Gov. of UK Expect Us!” reads a related tweet by Anonymous.

Assange, the founder and editor of whistleblower website WikiLeaks, has been ordered by Swedish authorities to be extradited from the UK where he had been under house arrest. Two women from Sweden have accused Assange of sex crimes, although he has yet to be charged.