How to detect a background program (in Windows 7) which steals active focus automatically?

The problem has been fixed. At a time of focus stealing, I pressed Alt+F4 and instantly spotted exiting process from Process Explorer.

Note: Windows Process Explorer can be downloaded as part of Windows Sysinternals library.

update: theres's any nice pogramm showing/logging, what process has focus: https://social.technet.microsoft.com/Forums/ie/en-US/dee98b15-0540-4975-b38d-ce3d2ee87c30/figuring-out-whats-stealing-window-focus

may this helps as well http://pcsupport.about.com/od/windowsxp/ht/stealingfocus02.htm

I used http://www.happydroid.com/focus and left the PC running over night to find the program that was stealing the focus.