Police are putting out a warning after seeing a rise in the number of men reporting blackmail threats after committing a sex act over the internet.
Five men in the Lynn and Downham areas have reported the blackmail threats to police over the last year.
The force has received a total of nine complaints from men across the county over the last year.
During 2014 there were four reports.
The victims had been contacted on social media websites and encouraged to commit a lewd act via a webcam by someone claiming to be a woman.
The men are then threatened to pay hundreds of pounds or face the risk of the pictures made public.
Chief Insp Stuart Armes is putting out a warning to people to be careful while using the internet.
He said: “If you are going to engage in a type of activity which you could be embarrassed about being made public, please think twice.
“If you control your behaviour, you won’t allow yourself to become a victim.”
Chief Insp Armes said this is a global issue with most of the potential blackmailers coming from the Philippines.
The blackmailers are able to use software to record a video or film the screen.
None of the victims, who are from a variety of age groups, have paid the blackmail threats.
Chief Insp Armes said: “Society has changed how it uses the internet. There are more people active on line than there were 10 years ago.”