Logout dialog/ log out prompt

Hi All,

I was wondering if somebody could help me. I would like to run a script when a user selects log out from the apple drop down to ask the user if they backed up their data before it allows them to log out. I created a script that prompts you and then brings you to the logout screen but do not know how to get it to run, or something similar to run, when you select log out. Obviously, I do not want it to run when the user has already logged out..

The other option I see that could work would be to change the message, "are you sure you want to quit all applications and log out now?" which I cannot figure out how to do.

Any help would be greatly appreciated

Thanks,
Marissa

 

By the way, the script so far is:
tell application "Finder" to display dialog "Please Backup Your Data

There is a risk of data loss if the machine experiences a hardware failure or an accident occurs" buttons {"Log Out", "Cancel"} default button "Cancel" with icon stop

if button returned of result is "Log Out" then
tell application "System Events"
log out
end tell
end if


The reason I need this script is because Users were storing files locally on a school machine and when the machines are re-imaged or incase of hardware failure we want to make sure that the student remembered to backup their data to their external hard drive.

We will not be erasing any content, we just wanted to remind students to backup every time they log out of their account

Thanks