Three Work and Income staff have been fired and six were given warnings after a review found employees had breached client confidentiality.
The review was launched after seven staff at the Manukau branch office were found to have inappropriately accessed clients' details and sacked last December.
The review took 100 randomly selected staff members from various regions and checked what systems each had accessed in the past year. Almost 10% were found to be in breach of client confidentiality.
One staff member has been sacked for e-mailing their partner about someone they knew who had applied for benefit.
Another has been dismissed for e-mailing a client's information to an associate in another government department, and a third for accessing and altering the records of people they knew.
The remaining six did not misuse client information but had no reason to be accessing certain files, the agency says.
Work and Income head Debbie Power says the Ministry of Social Development is taking steps to better educate its staff and monitor systems more closely.
Lessons for other departments - Commissioner
The Privacy Commission says all Government departments can learn lessons from the review.
Privacy Commissioner Marie Shroff says new technology has resulted in more people wrongly accessing other's private details.
The Labour Party says Work and Income has demonstrated great sloppiness in protecting confidential client information.
Labour's social development spokesperson Jacinda Ardern says better controls must be put in place to protect people's personal details.
She says Work and Income must do a follow up audit to ensure the steps it is taking to ensure client confidentiality are adhered too.