Government computers have been used to insert insults into Wikipedia entries about Muslims.
An investigation by the BBC revealed the phrase "all Muslims are terrorists" had been added to an article on veils.
The changes were made from a Whitehall IP address around October 2006.
Stevie Benton from Wikimedia UK, the charity behind the website, called the edits "appalling".
He added: "Wikipedia is the encyclopaedia that anyone can edit.
"This openness has led to an enormous reference work of great value.
"While vandalism does occasionally happen we are grateful to the many thousands of volunteers who write, edit and organise the content."
The news comes just a few days after it was revealed Whitehall computers had been used to edit the page for the Hillsborough disaster.
Changes to the entry on the online encyclopaedia include the phrases "blame Liverpool fans, "You’ll never wank alone" and "You’ll never walk again".
Margaret Aspinall, from the Hillsborough Family Support Group, said she was upset by the claims.
"I don't even know how to react, it's just so sad. I hear something like that and it upsets me a great deal, it makes me incredibly sad. I'm glad somebody has found out about it but I'm frightened to be honest that we haven't known until now."
In response to the latest controversy, the Cabinet Office reiterated its statement on the matter to the BBC.
A statement said: "The amendments made to Wikipedia are sickening. The behaviour is in complete contravention of the Civil Service Code. It is entirely unacceptable.
"The Civil Service Code applies at all times, and we take breaches very seriously. We have already announced an investigation to examine offensive edits to Wikipedia, and will look at other concerns raised."