Microsoft ASF videos can also "phone home"

[cassius () HUSHMAIL COM]

Using ASF editing software you can insert auto opening URL's at any timestamp
within a Microsoft ASF file.   The tag will cause your default browser to
open to the URL when that part of the movie is viewed.

This is not exactly hidden from the user but it could still be used to track
certain types of videos to IP addresses or to track the path of a copyrighted
movie through a internet distribution system.

-Cassius