Good Question. I don't know the answer, but assume it's the same as someone breaking in a taking paper charts.
I was reading about ways in which one can encrypt their data. There are various ways in which one can do this, one I read about is
http://www.truecrypt.org/.Additionally, offsite backup is essential in my mind. It won't help what's already gone, but at least I still have a copy of the documents.
Barbara