[asdxfg]

I know this is an old thread, but for reference sake of anyone who finds this thread:
To view drm files by the attribute columns in windows 7:
change the view to "details"
right click on an attibute column (eg. name,date modified, time, size) and click the option 'more'
Tick the box "protected" and click ok.

You can now sort files by DRM protection by using the "protection" attribute column