The browser was claimed to be "unsafe" between the October 12 and 19 last year, a study by Brussels-based ScanIT showed. Research found IE's closest rival, Firefox, was vulnerable for 15 per cent of last year.
"This means fully patched IE was known to be unsafe for an incredible 98 per cent of 2004," said ScanIT's CEO David Michaux.
"And for 200 days in 2004 - that's some 54 per cent of the time - there was a worm or virus exploiting one of those unpatched vulnerabilities," he added.
The company collated information from 195,000 internet users who checked their browsers for vulnerabilities using its browser security checker in 2004. The new results show a huge rise in the number of surfers using Mozilla's Firefox browser over IE since the company's previous report in 2003.
Microsoft was unable to comment at the time of writing.
As reported last month, The Mozilla Foundation announced an update to the browser to combat phishing attacks and other security vulnerabilities. The organization claims its browser has been downloaded 27 million times since it was released last November.