Editing your own entry on Wikipedia is usually the province of vain celebrities keen for some good PR. But a new website has uncovered dozens of companies that have been editing the site in order to improve their public image.

The Wikipedia Scanner, which trawls the backwaters of the popular online encyclopaedia, has unearthed a catalogue of organisations massaging entries, including the CIA and the British Labour party.

Workers operating on CIA computers have been spotted editing entries, including the biographies of former presidents Ronald Reagan and Richard Nixon, while unnamed individuals inside the Vatican have worked on entries about Catholic saints - and Sinn Féin leader Gerry Adams.

And somebody from a computer traced to US Democrat headquarters edited a page on conservative American radio host Rush Limbaugh, calling him "idiotic", "ridiculous" and labelling his 20 million listeners as "legally retarded".

But the biggest culprit that the scanner claims to have discovered is Diebold, a supplier of voting machines, which it says has made huge alterations to entries about its involvement in the controversial "hanging chad" election in the US in 2000.

The company was criticised in the wake of the disputed results, but edits made by its employees on Wikipedia have included the removal of 15 paragraphs detailing the allegations.

"In August 2003 Walden O'Dell, chief executive of Diebold, announced that he had been a top fundraiser for George W Bush," the deleted text read. "When assailed by critics for the conflict of interest . . . he vowed to lower his political profile."

The change, made two years ago, was quickly reversed and the culprit warned off for "vandalism". A Diebold official was not available for comment.

It is not the first time people have been found editing their own Wikipedia entries, which is considered a breach of etiquette on the website. Last year, some US congressional staff were found to be removing information they deemed unsavoury from the profiles of the politicians they worked for, and this year computer group Microsoft back-pedalled after it was revealed to have offered money to experts to "correct" entries about it on the website.

The scanner, built by Virgil Griffith, a researcher at the California Institute of Technology, works by comparing 5.3 million edits made on the encyclopaedia against the internet addresses of more than two million companies or individuals.