Parents were warned tonight that their children are not safe from paedophiles even in their own bedrooms as one of Britain's worst ever internet child sex abusers was jailed.
Postman Michael Williams, 29, used Facebook, Bebo and MSN Messenger to groom up to 1,000 children across Britain.
He used his trusted position in the community as a taxi driver and as a postman to target young girls on his rounds in Penryn, Cornwall, two of whom he later had sex with.
Truro Crown Court heard Williams persuaded at least 460 to perform sex acts on webcams for him which he recorded and kept on meticulously catalogued computer files.
Andrew Macfarlane, prosecuting, said Williams posed online as a 15-year-old girl called "Gorgeous Charlie" accompanied by pictures of a Ukrainian porn star and as a boy of the same age called James .
"The defendant has for many years groomed and corrupted hundreds of children across the country," he said.
"He utilised aspects of the internet so popular with children - Facebook, Bebo and MSN Messenger.
"The defendant ingratiated himself in the social networking sites of young persons, having gained their confidence, used questionnaires or simple conversations to encourage hundreds of children under the age of 16 years to perform sexual acts for him.
"This was internet sex offending on a previously unseen scale.
"Ironically, in this day and age, many parents don't let their children out at night lest they meet someone like the defendant.
"Instead, they feel they are safe in their bedroom but unknown to the parents some children were meeting the defendant using their computers. It is a chilling reflection."
Bisexual Williams was fascinated by child killers and police found cuttings about Soham murderer Ian Huntley at his flat.
"His sexual preferences are diverse and he has also deceived both male and female adults with his numerous false identities and has filmed, covertly, members of local football teams nude in the showers and young children changing on local beaches," Mr Macfarlane said.
Williams offered mobile phone top-up vouchers if girls posed topless for him on their webcams.
He also threatened other victims into keeping quiet about the sexual abuse, saying they would get into trouble because they were under 16.
"The defendant forbade one of the girls from telling anyone of their relationship, which disappointed her. He said that if people knew they would think that he was a paedophile because he was 12 years older than her," the prosecutor said.
Williams was also a local footballer and secretary of Falmouth Town Football Club. He abused these positions by installing a secret video camera in the showers and by abusing a 13-year-old boy.
He was only caught when one of his young victims, then aged 15, summoned the courage to contact police after finding disturbing child pornography on his computer. She was so shocked by what she saw that she was physically sick.
Judge Paul Darlow awarded her £500 from public funds for her courage in going to the police and the court was told that but for her actions children would still be being abused.
When Williams' flat was raided, police recovered four computers, tapes, CDs, USB sticks, a digital camera and video recorders. They found evidence he had filmed children getting undressed on local beaches.
One of the girls abused by Williams has been been left so traumatised by what has happened that experts believe she is suffering from Stockholm Syndrome.
Devon and Cornwall Police have identified about 500 victims he groomed or abused but believe there could be up to 1,000 youngsters in total because hundreds are too scared to come forward.
Following his arrest, Williams admitted that virtually all of the allegations were true.
"However, during all interviews he showed neither empathy or sympathy towards any of his victims, save on one occasion when he became visibly upset," Mr Macfarlane said.
"Disconcertingly at times he talked as if he was the persona of one of his invented people."
Williams, of Tresooth Lane, Penryn, Cornwall, admitted eight offences of sexual activity with a child, 13 of causing a child to engage in sexual activity, three of meeting a child following grooming, two of making indecent images and one of voyeurism.
All the charges were specimens, reflecting five years of constant internet grooming and he asked for another four cases to be considered which reflected a further 460 known victims.
"Your behaviour reflects a calculated, targeted corruption of prepubescent and pubescent girls and boys, aged 10 to 16," the judge said as he jailed him for eight and a half years.
"Your web of deceit and corruption has affected hundreds of children. The method you employed exploited children by a means you knew would be popular with them Facebook, Bebo and MSN Messenger.
"You created for yourself completely fictitious profiles, male and female, posing as the sort of person who might be attractive to those you were corrupting."
The judge said that Williams had abused his position as a postman, taxi driver and secretary of a football club to target children.
"All these gave you the access to and the trust of young children. In some instances your grooming led to sexual encounters which went as far as full intercourse," he said.
"The indictment names eight children but that does not include the unnamed anonymous victims of the child pornography you kept.
"Unnamed are the anonymous children named in the Taken Into Account.
"The report on the effect of your action on the child victims is harrowing and I cannot overlook the corrosive effects on their families, their schools and the community in which they lived."
Williams's former employer, Royal Mail, said it suspended him as soon as the police informed it of the investigation. He was dismissed after his arrest in February.
A spokeswoman for Facebook said the company had recently launched a £5 million campaign to improve safety for its users.
"This case serves as a painful reminder that everyone must use extreme caution when talking to or meeting people they only know via the internet," the spokeswoman said.
"Those who use the internet to groom young people are tenacious in their efforts and have shown that they will use every online and offline opportunity to make contact.
"Sadly, many of those targeted online do not even realise they are being groomed until it is too late."
Speaking after the case, Detective Inspector Simon Snell, who led the team investigating Williams, said he was "depraved" and "corrosive" and preyed on young people.
"Parents need to make sure their children are not using their computers in their bedroom as they have got no idea who they are speaking to," he warned.
"All of the victims in this case were using their computers in their bedroom."
Cornwall Council, Falmouth School and Penryn College and Cornwall and Isles of Scilly Safeguarding Children Board also warned of the dangers of internet use.
"The dangers of internet child abuse cannot be underestimated and no parent or carer should be complacent regarding the risks their child may be exposed to," they said in a joint statement.
"Our experience suggests that many parents and carers are failing to recognise the importance of ensuring their children access the internet safely.
"Parents and carers need to educate themselves about the risks posed by potential perpetrators through internet access and assure themselves that their child is safe."