.wmv files are 99,9% spam. That's why this file type has been added to the security filter. Even without this filter, you will hardly find any useful .wmv files on the net...
I still think it is better only block ip and not file names, perhaps add it as an option in the installer or improve the way a user blocks the content, improving the heuristics to detect spam, etc. And if not posible, filter wmv by size, most files are small. I have a custom list with wmv filter disable and no spam appears, I can send if they want to have it tested.
i'm against filtering all WMV or WMA - it's odd to expect something "interesting" from windows media files with size less then for example 20 MB, but many really interesting data on the network is in WM format.
And text-based filtering in security rules is very bad idea at all.
Bad that Shareaza don't have ability to apply multiply search filters like: block all WMV less then 50 MB and block all ZIP less then 2047 MB and block all AVI and MOV less then 50 MB and so on.
My dream is white list with allowed pairs "extension:size"