This flag indicates that the window that received this motion event is partly or wholly obscured by another visible window above it. This flag is set to true even if the event did not directly pass through the obscured area. A security sensitive application can check this flag to identify situations in which a malicious application may have covered up part of its content for the purpose of misleading the user or hijacking touches. An appropriate response might be to drop the suspect touches or to take additional precautions to confirm the user's actual intent.

[Android Documentation]