MS quite often lies about things that are "not responding"
Most of people think that "Not responding" means "program hangs". That IS NOT true.
Its not a Microsoft mistake. Instead, its a user mistake about the meaning of the message.

Every process that has a windows should "react" to windows events in a given time (i cant remember know how much time). When Windows detects that is a lot of windows events enqueued to a process, it marks that process as "not responding". When that queue fills up, Windows windows manager (or event manager i dont remember) just stop to try to send new events to that windows.
The kind of message is more a bad windows design (from the software vendor) that a Windows problem. When you write a Windowed process, you should give, from time to time, some process cycles to your windows task. On AK example (AntiVirus), AV is goind deeply on a nested packed structure (such as .cabs) and just stop (for a while) responding the "click" events (or other windows events, such as minimize, move and so on).
Never think that "not responding" means that "program stucked" and end it. Most of the times, is just a transient state.