On Monday morning the site's usual content of Labour Party news was replaced by an image of US President George Bush carrying his dog with Tony Blair's head superimposed on it.
The hacked material was removed from the site by 0945.
That meant visitors were again able to read the latest Labour Party news - on this occasion new health secretary John Reid's claim to have been "a Blairite before Blair was ever heard of".
BBC News Online technology correspondent Mark Ward said: "Parties across the political spectrum have one thing in common: their lax approach to computer security.
"The Labour Party isn't the first, and won't be the last, to be embarrassed like this."
Many prankster hackers and computer vandals used software tools that regularly probe the defences of websites to see if they suffer well-known vulnerabilities, he said.
Mr Ward speculated that an update to the Labour Party site had not gone as well as planned and gave the site-defacers their opportunity.
The sites of political parties were high on the list of many prankster hackers and computer vandals because any success would be widely reported and give the attacker the right to brag about their success, he added.
Article was found here http://news.bbc.co.uk/1/hi/uk_politics/2993550.stm