User Account Image Replaced Without My OK

Today I was using a wireless network at a car dealer while my car was getting fixed. Before connecting to this new network, I turned all my sharing options off.

When I came home, I noticed that the image on my user account had been changed, and not by me. How is this possible? I certainly didn't click on anything and there were no interface messages that appeared while I was connected. There's nothing in the Console logs that relates. I'm kind of worried about security now.

Has this happened to anyone else?

I'm running 10.7.5 on a MacBook Pro and all my software is up-to-date.