The worm does not cause any direct damage to the user's PC and uses its own e-mail engine to replicate itself to a user's contacts from their Outlook address book.
Anti-virus special MessageLabs said it had seen 174 copies in the past nine hours. According to Mark Toshack, virus analyst at MessageLabs, the virus started in Indonesia and has spread across the world.
The UK, the US and the Netherlands had the most infections, according to statistics from MessageLabs.
Toshack said the worm exploits an old vulnerability in Internet Explorer where an attachment opens automatically whenever a user previews an e-mail.
Microsoft had released a patch on 29 March 2001, but Toshack said there were still a number of users who had not loaded the patch.
"People with the older versions have not bothered to update," he said. Anyone running the latest IE software is automatically protected.