If you suspect a file to be malicious, you can send it to Microsoft for analysis. The Microsoft Research and Response will check the file for malware, which may include viruses, spyware, worms, trojans, rootkits, adware, etc.
Submit malware and suspicious files
You can submit the file directly to Microsoft using this webpage at the Malware Protection Center.
It is always recommended that you zip the file and send it in compressed form.
If you need additional support, visit the Consumer Security Support Center.
Incidentally if you wish to submit malware and suspicious files to antivirus companies, here are a few links which will help you:
If you know of any more, please do share!
X-ray a freeware that automates the proxess of sumbission of malware files may also interest you.