I recently installed the Windows 8.1 Update on a virtual-machine setup. In this case Windows is installed on Parallels Desktop running on a Mac using OS X 10.3 (the latest available version).

I have only a few programs installed on Windows 8.1. One is an auto-maintenance database program that's not available on Macintosh. The other is Quicken 2011 which I use because the Mac version of Quicken is crippled.

Today, I found that the data files from BOTH of these programs were simply gone, while everything else functioned apparently normally. The computer was powered down ever since these programs were last used successfully, so I couldn't have been hacked, and Norton Internet Security with the latest definitions is installed on Windows. In 24 years of PC use, I've never once had this problem. Both files were backed up, so I didn't lose data, but I don't know what caused this very weird phenomenon.

I'd blame the Windows 8.1 Update installation if anyone else noticed anything like this, but I cannot imagine for the life of me what would cause the selective deletion of data files from two different programs.