Defence publication, Army, reported that ADF members had used the internet to locate friends from previous postings, but some details about work history and current duties could be classed as official and therefore restricted.
A defence spokeswoman said the department took security issues seriously.
"It is important that our people know why and how to practise good security," she said.
"Once information is on the internet it can be accessed by anyone.
"It can be used for purposes never intended by the person who made the information available."
Defence was asking personnel to exercise good judgment in the details they provided.
"We are simply asking our people to exercise good judgment in providing information about the work they do in defence," the spokeswoman said.
