Netsafe says the internet is increasingly being used as a means to blackmail and threaten people.
Online 'trolls' - people who deliberately hack or threaten other users - have recently infiltrated the Dunedin Buy Sell and Trade's Facebook page.
Photos have been lifted off profile pages and threats made that they will be published on pornography sites unless money is paid.
Netsafe executive director Martin Cocker, says online harassment and blackmail attempts is on the rise.
He says 'trolling' on social networking sites like Facebook is becoming more sinister.