Almost 80 people including a Scout leader, a retired teacher and members of the Armed Forces have been arrested in raids as part of an operation targeting suspected internet paedophiles.
Officers from more than 40 police forces executed more than 143 search warrants in England, Scotland, Wales and Northern Ireland in the 48-hour operation led by the Child Exploitation and Online Protection Centre (Ceop).
Some 80 children were "safeguarded" following the raids. One in four were found at the properties searched by police. More than 30 cases were referred to child services.
Most of the warrants related to image offences, including the possession and distribution of indecent pictures of children, Ceop said.
Among those arrested were a referee, a pathologist, Government employees, a firefighter, an outdoor activities instructor and a computer programmer.
Known offenders who had breached the conditions of the sex offenders' register were also among the 78 people arrested in the dawn raids on June 12 and 13. That number could still increase as Ceop wait for reports from two more police forces.
In video footage of one of the raids, officers in plain clothes can be seen placing laptop computers into evidence bags.
They also seized USB storage devices and external hard drives, digital cameras and any other items capable of storing pictures.
Andy Baker, deputy chief executive at Ceop, said the pictures on them would be scrutinised to see if the background revealed any clues to the identities of the victims.
"Every image is a crime scene, we need to identify that crime scene," he said.
Ceop also published a report warning that anyone caught downloading child abuse images online poses a risk of committing physical sex attacks on children.
The report said that one analysis showed 55% of paedophiles who possess indecent images also commit sexual offences against children.
Kate Fisher, a principal analyst at Ceop, said: "The images being downloaded are increasingly becoming more extreme, sadistic and violent, and feature increasingly younger children."
However, the severity and number of images held by offenders are not enough alone to assess the risk they pose or the sentence they should receive, the report said.
Ceop urged police forces to prioritise the investigation of anyone caught with child abuse images who has easy access to children.
Ms Fisher said the dramatic increase in images being downloaded, and the cuts to police resources, meant officers struggled with the workload but stressed that the notion that any case may result in the identification of a victim should be at the forefront of every investigation.
She added: "The levels of austerity and the caseload of indecent images of children is unprecedented. A quick and timely investigation for each case is increasingly unrealistic. Victim identification is the key element."
Almost 100 case studies from 34 forces found offenders who both possessed child abuse images and attacked children were "almost exclusively white males", most aged between 19 and 45.
One offender was found with 2.5 million still and moving images.
In 85% of cases, offenders looking at indecent images of children did so at home, with the rest looking at images mainly at work. More than half of those living with a spouse or partner were also living with children.
Andy Baker, deputy chief executive at Ceop, said: "It is clear that those who possess indecent images also pose a significant risk to children, and understanding and managing that risk is not an easy undertaking."
He called for the authorities to look beyond the quantity and severity of the images, adding that a full risk assessment should be considered before a judge hands down any sentence.
Referrals to Ceop increased by 181% between April last year and March, figures showed.
The report, entitled "A Picture of Abuse", said it was "increasingly unachievable" for officers to investigate such cases.
"In a perfect world all IIOC (indecent images of children) possession cases would be subject to a comprehensive, quick-time investigation as soon as intelligence comes to the attention of law enforcement.
"However, in a time where resource is sparse and priorities continually modified, this has become increasingly unachievable."
It warned: "There is a clear correlation between IIOC offending and contact sexual offending against children although causation cannot be established.
"Anyone who possesses IIOC poses a risk of committing contact sexual offences against children.
"Cases where it has been identified that an IIOC possession suspect has access to children should be actioned as an immediate priority."
Access to children was a "key factor in the assessment of an offender's risk" and the link between possessing the images and carrying out sexual attacks "highlights the need to consider each possession offender as a potential contact offender to some extent", the Ceop report found.
Devon and Cornwall Police executed three warrants as part of the nationwide operation.
"This resulted in two people being arrested and a third was interviewed as a voluntary attendee," a force spokesman said.
"A quantity of computer equipment was seized for analysis and a number of children were safeguarded through these actions."