The number of sexually-related cyber extortion cases in Singapore involving foreign female suspects has more than quadrupled to about 50 cases last year, local media reported on Thursday. There were only 11 such cases in 2011, the police said. The victims are often men, typically students, full-time national servicemen or working adults who meet the women on social networking sites such as Tagged.com and Facebook, and add them as friends. They are then persuaded by the women to strip and masturbate when they see the women naked or dancing. Once the men are naked, usually while on a video call with the women \"friends,\" the women end the session abruptly, claiming someone is at their door, the Straits Times said. The men later receive a message from the women, informing them that video footage had been taken of them in sex acts. The women then demand money and set deadlines for payment. Sometimes the men are given a link to a YouTube clip of their \" performance\". It is not known how long these videos stay \"live\" in each case. Some perpetrators back away from demanding money when the victims say they will go to the police. The foreign women, from countries such as the Philippines, South Korea and Japan, usually operate from their home countries. According to the police, more than 1,200 Singapore dollars (968 U.S. dollars) was transferred by victims in 2011, and the number rose to 1,700 Singapore dollars (1,371 U.S. dollars) in total. The transfers were made using PayPal, they added. The police urged the public to be wary of messages from unknown people who want to befriend them online. Internet users should not fulfil any requests that put them in vulnerable positions, such as performing compromising acts in front of a webcam, or giving personal details about themselves. Those who become victims of such attempts should call the police immediately and should not remit or transfer money that has been requested, it said.