Secunia - Advisories - Internet Explorer File Download Extension Spoofing

Now this one is interesting:
Secunia - Advisories - Internet Explorer File Download Extension Spoofing

Description:
http-equiv has identified a vulnerability in Internet Explorer, allowing malicious web sites to spoof the file extension of downloadable files.

The problem is that Internet Explorer can be tricked into opening a file, with a different application than indicated by the file extension. This can be done by embedding a CLSID in the file name. This could be exploited to trick users into opening "trusted" file types which are in fact malicious files.