There are two levels of modality for system-modal message boxes-soft modal and hard modal. A soft-modal message box does not allow keystrokes or mouse input to reach any other window but does allow other messages, such as deactivation and timer messages, to reach other windows. A hard-modal message box does not allow any messages to reach other windows. A hard-model message box is appropriate for serious system warnings.

To create a hard-modal message box, combine the MB_ICONHAND style with the MB_SYSTEMMODAL style. To create a soft-modal message box, use the MB_SYSTEMMODAL style with any style other than MB_ICONHAND. The MB_SYSTEMMODAL icon always is in memory and is available even in low-memory situations.