How does the draggable crosshair in Process Explorer work?

There is a feature in Sysinternal's Process Explorer that allows a crosshair to be dragged from the application to a control in any other application you are running and highlights said control.

Does anyone know how this was achieved or if there is a .NET/C++ library out there that can be reused?

Using Win32 API

• GetCursorPos: to get the cursor position (maybe .NET has its own function to do that)
• WindowFromPoint: to get the handle of the window from a specific point in the screen

more info