Hundreds of potential victims of a man accused of hacking into children's online accounts and forcing them to perform sexual acts on a webcam have been urged to come forward.
The rare appeal comes as a man is being held in custody in Kuwait accused of befriending young victims online and threatening to reveal personal information to family and friends unless they continued to perform sexual acts on a webcam.
The Child Exploitation and Online Protection (Ceop) centre, which has co-ordinated the international investigation, said there could be hundreds of young victims in the UK, adding that police believe the abuse has been going on for three years.
The investigation involved the FBI in the United States, as well as police forces in Canada, New Zealand and Spain, among others, Ceop said.
A dedicated NSPCC helpline has been set up on 0800 614 458 for anyone who thinks they may have been a victim.
The inquiry was prompted in March when officers from West Yorkshire Police contacted Ceop regarding a suspect who had targeted a young girl online.
Police enquiries established a number of victims who described performing sexual acts online, Ceop said.
"Generally, the offender's method has been to use an instant messenger service and pretend to be a friend of the targeted victim," a spokeswoman said.
"During subsequent conversations, the offender directed victims to an internet link. When clicking on this link, victims were asked to provide their e-mail account and password, allowing the offender to take control of their login information.
"The offender was then able to take control of and hack of the victims' accounts, changing their passwords and security information.
"The offender would then inform the victims' that their account had been hacked and they no longer had control of it.
"The offender continued the threats, saying that personal information about them would be sent to friends and family on the internet, unless they continued to perform sexual acts via the webcam."