This morning, I went to open a PDF only to discover that SumatraPDF had disappeared. All of the other files in the installation directory were there, only the executable was missing. Wondering if perhaps it had somehow been quarantined by my anti-virus, I discovered that the same fate had befallen Panda Antivirus, all of the files were present except the primary executable. So far, I've noticed the same fate having befallen Winamp and Calibre as well, The bulk of my applications remain untouched, however.
The first thing I did was run a scan with a fresh installation of Malware Bytes but it didn't find anything. I then reinstalled Panda and that scan came up clean as well. I did a check disk on the C: drive but no disk errors were detected.
I had been contemplating doing a fresh install anyway (possibly switching Windows 8 to my faster primary hard drive as motivation to use it more) so I'll likely be doing that soon. (I have Ghost images of the drive, as well.) But I've never seen behavior quite like this before and would like to get to the bottom of it. Any suggestions?