The Conservative Party has deleted speeches and press releases published on its website between 2000 and the 2010 general election.
The archive has also been hidden from search engines.
The Conservatives said the move keeps their revamped website up-to-date.
Computer Weekly said the effect of the changes was "as alarming as sending Men in Black to strip history books from a public library and burn them in the car park".
"Prime minister David Cameron and Chancellor George Osborne campaigned on a promise to democratise information held by those in power, so people could hold them to account," it added.
Instead, they have overseen a change which has left Conservative speeches in a "secretive corner of the internet like those that shelter the military" and "gangsters", it concluded.
Archived pages on the Conservative Party website providing a record of evolving policy announcements were deleted "sometime after 5 October", Computer Weekly said.
In addition, a text file was added to the website, called "robots.txt". This is a standard way of telling search engines which parts of a website they should not try to index.
But the robots.txt file had the effect of preventing search engines from continuing to make a record of the website's former contents available to the public.
It also prompted the Internet Archive to take down its copies of the pages, according to Computer Weekly - although some of those copies have since been re-instated.
A Conservative spokesman said: 'We are making sure our website keeps the Conservative Party at the forefront of political campaigning.
"These changes allow people to quickly and easily access the most important information we provide - how we are clearing up Labour's economic mess, taking the difficult decisions and standing up for hardworking people."
Labour MP for Edinburgh East Sheila Gilmore described the changes to the Conservatives' website as a "cynical stunt" saying "it will take more than David Cameron pressing delete to make people forget about his broken promises".
Update 25 November, 2013: The Conservative Party has pointed out that many of the web pages can be found on the British Library's UK web archive.