The easiest approach would be to handle the MouseMove event of each HtmlDocument that was loaded, but it doesn't work over embedded objects in document like the many Flash ads you see in just about all webpages... so they probably use a system wide Mouse Hook.

By the way, you're not getting messages to Wndproc because the Webbrowser control is a wrapper for an ActiveX control that hosts the rendered document object, so even with a NativeWindow class to get messages from the COM component you'd have trouble finding the correct window handle to listen for.

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