Read this post coming from the Silverlight SDK blog to find out more about the Silverlight support for output protection.
The purpose of output protection is to increase content protection during transmission between a computer’s video or audio output port and the input port of another device such as a monitor or set of speakers (output). This is useful to prevent someone from intercepting copy protected content “en route” between such devices, known commonly as an "analog hole".
Output Protection is specialized stuff and so this post will be a bit arcane to most, but will hopefully be useful to a few folks out there who are familiar with OP and want to integrate it into their Silverlight apps.