Much of today's modern operating systems are arcane black boxes that no one but the most experienced computer users know. Not that most users know where to look or have access to some folders anyway. So when a system app silently fills up a hidden folder with trash files, most users might not know where to look. This recent incident plaguing some Windows users isn't actually the work of some new malware. Instead, it's actually the fault of Microsoft's own Windows Defender, a buggy Windows Defender at that.