I had an email from a partner of ours who was looking to stop a user from changing the time on a Windows Mobile device.

I discovered that this can be achieved quite easily by modifying the following registry key.   HKLM\Software\Microsoft\Clock\AppState

If it’s 11 hex they can change the time – if it’s 10 hex the clock applet won’t run.

 

This then lead to a broader discussion of whether it is possible to prevent certain applications from being run.  My colleague Rabi Satter directed me to a great blog article he has written which describes how to setup a list of programs that are not allowed to run regardless of whether they have valid certificates or in ROM.

http://www.satter.org/2007/03/lets_shell_some.html