Detecting workbook activation

[Jack Wolf]

I am a college professor and I am trying to develop a set
of macros that will let me try to prevent potential
cheating when students take exams and are allowed to use
Excel.

Specifically, I would like to prevent them from loading
other Excel files (in case they try to open their homework
and copy and paste it into their exam workbook) and from
opening other applications (like email, instant messenger
or anything else where they could write out answers.)

I have not been able to figure out how to lock out those
actions and I suspect it would take programming at a
deeper level (i.e., Windows rather than Excel) so my next
thought was simply to lock the workbook if they deactivate
it and warn them that once they leave the workbook, they
are done with their exam. [I will have passwords to unlock
the workbook so it can be graded or if a student has their
file deactivated by accident.] I have been able to get
this to work detecting when you deactivate one workbook
for another using the workbook level Activate and
Deactivate events but I haven't been able to detect when
you leave Excel for another application and then come back.

So, what is the best way to detect if a user has
deactivated Excel completely and then reactivated the
application?

Thanks in advance,
Jack