Ten Whitehall departments including the Ministry of Defence, the Department of Health, and the Department for Business, Innovation and Skills are still using Internet Explorer 6 (IE6), contravening the government's own security advice.
IE6 has had a number of security alerts over the last year and upgrading to version seven or eight is considered basic security practice by experts and is free of charge.
Get Safe Online, the government's online security advice service, recommends upgrading as the first step in ensuring safe online browsing.
"The first thing to do is to make sure you’re using the latest version of Internet Explorer. We recommend running the latest version because it includes many security features that were not present in previous versions," says the organisation's web site
Other departments that have not upgraded include the Department of Communities and Local Government, the Scotland Office and the Equalities Office.
Departments that have not upgraded completely but intend to in the near future are the Department for Transport, the Ministry of Justice, the Department for Children, Schools and Families, the Department of Work and Pensions and the Department for Culture, Media & Sport.
The only departments to have upgraded from IE6 are the Department for International Development, the Department for Environment, Food and Rural Affairs, the Foreign & Commonwealth Office, and the Northern Ireland Office.
The revelations come after a series of parliamentary questions from Tom Watson, who stepped down from his role as minister for digital engagement earlier this year.
The Treasury, the Home Office, the Cabinet Office and the Department of Energy and Climate Change have yet to reply.