Surfers of online adult internet sites are being warned to be wary after a number of incidents where people engaged in sex sites have become victims of extortion.

Detective Senior Sergeant Ross Patterson says detectives have so far dealt with two victims but suspect there may be several more who haven't come forward.

Police are investigating two incidents were people have become victims of extortion after engaging in online sex sites.

'It appears overseas based fraudsters are preying on New Zealanders who engage in online sexual activity and once they have made contact with the person, cash is demanded.

'The demand for cash is accompanied by a threat that explicit footage of the victim engaged on the adult site will be uploaded on social media sites if money is not paid over.”

Ross says one of the main challenges for investigators is that the complaints of extortion are difficult to pursue as the offenders are based overseas.

'So we are issuing a broad warning to users of internet based adult websites to be aware, it appears users are being watched and they may become a victim of attempted extortion.”

People who have fallen victim to such criminal activity can contact their nearest police station.

Alternatively, information can be left anonymously via the Crimestoppers 0800 555 111 line.