Your server appears to have been compromised by the Nimda mass mailing worm. It uses various known IIS vulnerabilities to compromise the server. Anyone visiting compromised Web servers will be prompted to download an .eml (Outlook Express) email file, which contains the worm as an attachment. Also, the worm will create open network shares on the infected computer, allowing access to the system. During this process the worm creates the guest account with Administrator privileges.

Take this server offline immediately, rebuild it and apply ALL vendor patches and security updates before reconnecting server to the internet, as well as security settings discussed in Additional Information section of Microsoft's web site at http://www.microsoft.com/technet/security/bulletin/ms01-044.mspx Check ALL of your local Microsoft based workstations for infection. Note: this worm has already infected more than 500,000 computers worldwide since its release in late 2001. See: http://www.cert.org/advisories/CA-2001-26.html