So, remember what Radio buttons are for? You know, these things:
They have one specific meaning: select one.
But in MS Security Essentials, they decided to give them the functionality that tabs have. I guess it's because the window already had tabs in it, so they decided "ok we need another selection level."
Those radio buttons, in this case, select what gets displayed underneath.
But the original mistake wasn't using radio buttons for this purpose. That's what happened when the design group wrote itself into a corner by using tabs already. They knew they couldn't get away with having nested tabs - not anymore, anyway. The original mistake was using tabs for "Home, Update, History and Settings" in the first place. Those items don't have the right relationship to each-other to form a proper tab group. They don't belong together that way.
They were probably placed there together, uncomfortably, because the design team didn't want to be guily of making another app with menus in it. They probably didn't think they had enough menu items to warrant a traditional menu bar. So they used even more space to do the same thing and locked themselves out of using tabs further down the window.
Investigating the problem in the other direction: why are the three conditions of history separated like this? Why not just colour-code them in the list, or use checkboxes instead of radio buttons so that the viewing window could just be a typical filtered list, which people do understand?
