Did you know that the privacy act has limitations.
What can happen is that legal bodies can subpoena your details (past addresses, tax records any of that stuff) in court proceedings from other agencies. So therefore docs can obtain all sorts of details about you to paint a picture they are trying to portray about you.

I personally encountered this when I was scared of the father of my child and did a runner, moved house, silently listed etc etc - went to great lengths, sought legal assistance about all this.

And even after all that some months after the child was born I get a knock on the door. I answer the door. A man (baliff) says I am here looking for ............ I say that is me, but who are you and how did you find me? He replied and showed me where it stated that the father's solicitor had subpoened the address and other necessary detail from centrelink to tract me down to get papers served on me so that the father could then face me in court and apply for access to this child.
There was no proof that this 'father' was the biological father either.
This is scarey that this can happen. It never used to be able to occur. I believe that for eg victims of domestic violence could get a complete new identity and be safe. Not any more.