Did you upgrade Mavericks to 10.9.3 the other day? You may or may not have noticed a “little” bug, introduced by iTunes 11.2:
Thursday’s iTunes 11.2 release contained a bug that was both inconvenient and risky: If you have Find My Mac enabled, your Users folder (/Users) will be hidden at startup. Worse, that folder, along with /Users/Shared, will have their permissions set so that anyone can modify them, creating a security risk.
PYBT for Dan Frakes’ helpful post on Macworld: Apple issues iTunes update to fix /Users issue