Computer hacking collective Anonymous claims it has attacked a number of Government websites in protest over the Julian Assange case.
Websites including that of the Home Office and the Ministry of Justice were affected by the group, which has been using the hashtag "OpFreeAssange" on Twitter.
WikiLeaks founder Mr Assange, who is wanted in Sweden for questioning on sexual assault allegations, has been seeking refuge in the Ecuadorian embassy in London for two months with the British authorities threatening to arrest him if he steps outside.
A Ministry of Justice spokeswoman said: "The Ministry of Justice website was the subject of an online attack last night at around 2000 hours.
"This is a public information website and no sensitive data is held on it. No other Ministry of Justice systems have been affected."
A spokeswoman for the Home Office denied its website was "hacked", but added: "It was targeted by protesters on Monday night but only experienced very minor interruption to the service.
"We had measures in place to protect the site and no other Home Office systems were affected."
It is the latest development in the diplomatic row between the South American country and the UK.
Ecuador's president Rafael Correa said it would be "suicide for Great Britain" if authorities tried to enter his country's embassy to reach Mr Assange.
Speaking on state television, Mr Correa said such a course of action would be "suicide for Great Britain because then people could enter their diplomatic premises all around the world and they wouldn't be able to say a thing".