Question : Windows messages : How to find the sender of of WM_USER message

Hello everyone,
I am having trouble with one function of my view.
This function is called on a windows message WM_USER + 100.
My problem is that my view is receiving the message again and again.
I can't find what part of the software is sending that message.
I used Spy++, but I don't know if I can use it to find the sender of the message.
It tells me correctly that my view is receiving the message but not who sent it.
Is Spy++ able to do that ? How can I find the sender ? Do you know another tool to use for that purpose ?
Thanks.

Answer : Windows messages : How to find the sender of of WM_USER message

Wow... good question.  
Spy++ does not appear to record the source process or thread, nor is that available with a message hook.  

Any process can send any message to any window and remain anonymous while doing so.  Until recently, that's been a security issue with System Services that expose a U/I -- some outside program could pull the strings of the Service, and thus obtain elevated privileges.  

However, If I were you, I'd not suspect outside programs until I'd ruled out my own program and even controls (such as RichEdit) that are outside of your direct control.   WM_USER+100 is a common value -- its usually safe to assume that a standard window (such as a button control) will ignore it.  

However, I know that MFC uses, for instance, WM_USER+101 in its CMFCPropertyGridCtrl intenal handling, so I can't rule out +100 (though I can't find it in the MFC source files).

You might be able to get a clue by looking at the lParam and wParam.