Windows calls a WH_CBT hook procedure before activating, creating, destroying, minimizing, maximizing, moving, or sizing a window; before completing a system command; before removing a mouse or keyboard event from the system message queue; before setting the input focus; or before synchronizing with the system message queue. The value the hook procedure returns determines whether Windows allows or prevents one of these operations. The WH_CBT hook is intended primarily for computer-based training (CBT) applications.
For more information, see the CBTProc function.