Use WUA to detect when updates occurred?

I have a program that I run all the time in the background and would like to
receive notifications of when Windows Updates have been installed. How would
I go about doing this? That is, a user runs Windows Updates and then my
program either polls some value or gets notification that the updates are
complete and then I do something in my program. I've been trying to find
something in the "Windows Update Agent API" (WUA) documentation to do this
but I'm kinda lost. If someone has a VB script to do what I'm after or just
get the last timestamp updates were installed on the system, I'd be really
grateful.