How can you make soldiers and families understand there not such thing as a "private message on facebook?

[Michael C]

What is the best way to show are soldiers that there is not such thing as a "private message" on facebook? and that they should not use their real names on facebook? I have told them them until my face was blue that there is not such thing as a "private message" those of us with intelligence background know better. So many family members are telling so much personal information, enough for the wrong person to do damage. What does it takes for them to understand that all that you say on facebook or any "internet/cell phones" is public property? that this information is sold out to the highest bidder for comercial purposes as well as other money making schemes?