title: Show only one instance of messagebox.show in c#
body: <p>I have a created a custom keyboard shortcut for my application,
  when the user press combination keys of CTRL + ALT + Q, i show
  a messagebox "Are you sure you want to log out ?" Then if clicked
  YES, i log out of the application.</p>
  
  <p>Problem :
  I want to make sure that, only once instance of message box shows.
  No matter how many times the user presses the shortcut.</p>
  
  <p>currently it shows multiple message box, on pressing multiple 
  shortcuts.</p>
  
  <p>How to overcome this ?</p>