JS/Except-Fam is a Trojan which exploits a vulnerability in Microsoft VM ActiveX component.
If an affected web page is opened, a JScript embedded on the page attempts to use the vulnerability in order to drop files on a local drive, change registry keys without the user's knowledge or perform any other malicious action on the local machine.
For more details about the Microsoft VM ActiveX component exception vulnerability please see Microsoft Security Bulletin MS00-075.