Methods to verify that security patch is installed correctly and functioning

All,

Does anybody know of how to verify that security patch is installed
correctly and functioning? A quick way would be to check to see if the
QFE numbers are listed in the registry of the build image. But this
doesn't verify that security patch is working or not. It only gives
that it is installed.

I would like to know if there is a 3rd party application that will
verify that it is working, (not just installed).

Ju