I and several friends always have our personal profiles set to Friends Only. Now I know that if you do set an individual status update to go out as Public, it will automatically reset your default Privacy settings from Friends to Public and you have to go back in again and change it back.
However, I had not done that.
It was only today that I noticed what had happened. For nearly five days, all my updates had been going out to the world and his wife without my knowledge and without any explanation or warning from Facebook.
For those of you who do not know how to set your privacy. Click on the padlock to the top right of the toolbar and change who can see your posts to Friends rather than Public.