Snooping my files? Ugh, jackasses. But using ROT13 to hide your activities? That's downright offensive. Who the hell uses a Caesar cipher in the 21st century?
Actually the UserAssist reg key is meant for windows explorer usage tracking and does the ROT13 encoding automatically. You can turn off the encoding or tracking in general. Source-http://www.aldeid.com/wiki/Windows-userassist-keys
It worked for quite I while I would guess, months or maybe years they got away with it.