While i was working in a creative world, a friend tried to join the world I was in. Upon doing so, without ever being able to join, we both received a message displaying "Wow this server is popular! Check back in later..." After clicking ok, my world was no longer available in my list of worlds to play. I went into the file folder where all my local worlds are stored, and it was not there. I right clicked and hit properties, went to the Previous Versions tab to see if it was deleted there so I could restore it, but it said nothing had been deleted. My creative world was completely gone without a trace. All because a friend attempted to join the world without my directly inviting them. The world was an open world for any of my friends to join.