Responding to the critical status of the vulnerability, Microsoft issued a patch to protect users of their older operating systems.
Until yesterday (Tuesday) the thousands of users who had not updated to, or were not using Windows SP2 remained vulnerable.
Users of Microsoft Windows 98, XP SP1 and Windows 2000 are urged to update as soon as possible. Those operating on these systems and using the Opera or Mozilla browsers are not affected by the exploit. If infected the Bofra worm allows external users to access the computer, sends itself to email addresses stored on the computer and downloads code form the internet.
The Bofra worm marks a highpoint in vulnerability exploitation. Within four days of the iframe problem being announced it was out in the wild and is seen by some as an indication of the final step towards zero-day exploits.