People who used adult sex websites are being targeted by extorters, police say.

Detective Senior Sergeant Ross Patterson of the Hamilton CIB said detectives have dealt with two victims but suspect there may be more.

"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," Mr Patterson said.

"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."

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Mr Patterson said it was difficult investigating such complaints when fraudsters 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."