An HIV positive paedophile who groomed teenage boys on the internet and filmed himself having sex with his victims has been jailed for life and told he must serve at least 10 years before he is considered for release.
Anthony Marsh, 53, was jailed at Sheffield Crown Court along with another paedophile, Lee Davis, 39, who was also given a life term and told he must serve at least 12-and-a-half years in prison.
Judge Julian Goose QC told Marsh and Davis they were "predatory, dangerous paedophiles".
Police have described their activities as "vile, horrendous offences".
The pair, who are both married with children, used social networks such as Facebook and Bebo, as well as specialist gay websites, to befriend boys.
After grooming teenagers as young as 13 online, salesman Marsh and unemployed Davis met their victims and sexually abused them.
Police found a library of films hidden in the cellar of Davis's home showing him abusing the boys.
Officers also established that Marsh distributed some footage shot by Marsh over the web.
Speaking outside court, Detective Inspector Delphine Waring, of South Yorkshire Police, said: "Today's sentencing brings to a conclusion one of the most shocking series of sexual crimes committed against young boys that South Yorkshire Police has investigated.
"Marsh and Davis indulged their own depraved and criminal desires for many years against a number of young, impressionable and vulnerable young boys the length and breadth of the country.
"The extent of their offending was matched only by the duplicity of their behaviour, which included their use of pseudonyms and multiple mobile phones to disguise their true identities and the deceit they exhibited day after day to their own families."
Ms Waring said Marsh's crimes were "especially deplorable".
"Knowing he had HIV, he chose to engage in sexual conduct with teenage boys and, in so doing, demonstrated a complete disregard for their wellbeing and future health.
"But, for Marsh and Davis's victims and their own families, today's sentencing will not be the end of the story.
"The damage these two men have inflicted will last for many years to come."
The detective said it was possible more victims had not yet identified themselves and urged any people in that position to come forward for help.
Marsh, of Menson Drive, Hatfield, near Doncaster, and Davis, of Rowena Road, Conisbrough, near Doncaster, admitted a string of offences in September.
The judge heard how they were were both family men - Marsh a father of two and Davis a father of one - whose wives and children had no idea of what they were doing.
He was told how t hey spent hours online grooming their victims, most of whom were young teenagers coming to terms with their sexuality.
The judge made particular reference to their youngest victim - a 13-year-old from Lancashire - who was initially abused by Marsh in his own bedroom at home and then, later, raped by Davis after Marsh had passed on his details.
Davis recorded his abuse of the boy on a 45 minute long video tape which, the court was told, clearly shows the youngster, in his teenager style bedroom, pleading with the defendant not to do what he is doing.
Judge Goose heard how the boy was particularly vulnerable as he had recently come out as gay and been self-harming and subjected to bullying which was so bad he had tried to set fire to his own bedroom.
He said the burns from the incident were clearly visible on the film Davis made.
"Yet both of you groomed him and used him for sex," the judge said.
"You, Davis, raped him. And video-ed it."
The court heard how the pair were caught after Marsh was arrested in May 2012 at a hotel in Scarborough, North Yorkshire, when he was spotted with indecent images of children.
Police eventually found thousands of images in Marsh's possession. The judge heard many were at the highest possible level and involved sado-masochistic sex with children as young as six, sometimes involving animals.
The court heard there was no evidence Marsh had abused children younger than 13 but internet chat recovered by police indicated he was also interested in much younger children.
The offences admitted by Marsh and Davis started in 2004 when Marsh was already diagnosed HIV positive.
Judge Goose said it was "truly shocking" Marsh had unprotected sex with young, vulnerable victims knowing his condition.
He told the defendant he carried on "never for a moment telling most of them, any of them, of your diagnosis or telling them of the risk they were taking."
The judge said to them: "You are both predatory, dangerous paedophiles."
He told Marsh and Davis that the minimum terms he had given them reflected sentences of 20 and 25 years respectively that he would have passed if he had not decided to impose a life term on each of them.
Ms Waring has said there was no evidence Marsh and Davis knew each other before they met online but they began to work together pooling information on potential victims.
She said she was confident that the pair were not acting as part of a larger paedophile ring.
The court today heard of a series of incidents in which the pair would take their victims to woods, or Davis's van or even their own bedrooms, when their parents were out.
Davis and Marsh would used pseudonyms on the web but did not pose as teenagers as they utilised a range of social networking sites and communication sites including Facebook, Skype and Grindr.
The court also heard how Davis had a secret "dirty phone" and had sent and received more than 40,000 texts, following up his internet activity.
The pair appeared before a judge at Sheffield Crown Court on September 27 and admitted conspiracy to commit sexual activity with children, meeting a child following sexual grooming and number of other sex offences - 55 charges in all. Davis admitted further charges relating to indecent images today.
Marsh, who also used the names Tony Taylor and Tony Smith, admitted sexual activity with a child and possessing and distributing indecent images of children.
Davis, who Marsh knew as James Parkin until after they were both arrested, admitted raping a 13-year-old boy, sexual activity with a child and taking indecent photographs of a child.
Marsh's convictions involved seven boys. Davis's convictions involved six boys. Four teenagers w ere abused by both defendants.
The conspiracy charge admitted by both men involved the contacting of young men to facilitate meetings for sexual offences between May 2004 and June this year.
Both men sat next to each other in the dock today wearing open-necked shirts and flanked by two security officers.