The scale of his offences shocked authorities, with police believing as many as 3,500 children were targeted by McCartney on 64 devices.
McCartney used false identities online to befriend and exploit victims, primarily using Snapchat.
McCartney used false identities online to befriend and exploit victims, primarily using Snapchat.
The 26-year-old occasionally used other platforms, including Instagram and Kik.
Posing as a young girl, McCartney lured victims into sending intimate photos. He often used pictures obtained from other young girls to deceive new targets.
McCartney would then blackmail the children into sending more extreme photographs, threatening to expose them to friends and family if they refused.
McCartney's also put pressure on his victims to involve younger siblings, family pets, and objects.
McCartney's also put pressure on his victims to involve younger siblings, family pets, and objects.
The 26-year-old's relentless approach included using a template of messages to copy and paste to his victims.
He kept meticulous records, including screenshots of victims' Snapchat location pins to track their whereabouts.
In some cases, McCartney would go on to share images with other prolific paedophiles.
The court also heard that the harm caused was "unquantifiable" after McCartney "degraded and humiliated" victims for his own sexual gratification.
The judge stated that McCartney's actions had "changed forever" the lives of his victims.
The judge stated that McCartney's actions had "changed forever" the lives of his victims.
Cimarron Thomas, 12, from West Virginia in the United States, shot herself with her father's handgun in 2018.
The young girl's father, US army veteran Ben, killed himself just 18 months later.
Other children pleaded with McCartney after sending a photograph of a "self-inflicted cut".
The 26-year-old callously replied: "I don't give a s**t."
Responding to another child who feared they were about to die, McCartney wrote: "I don't care."
A Snapchat spokesperson expressed sympathy for the victims and outlined the platform's protective measures.
A Snapchat spokesperson expressed sympathy for the victims and outlined the platform's protective measures.
These include removing violating content, locking offending accounts, and reporting cases to authorities.
Snapchat has implemented additional safeguards for teenagers, making it harder for strangers to contact them.
The platform has also expanded in-app notifications to encourage teens to communicate with trusted individuals.
The platform has also expanded in-app notifications to encourage teens to communicate with trusted individuals.
Parents can monitor their children's Snapchat activities through the Family Centre feature, which allows them to see their teens' contacts and friends list.
These measures aim to prevent future cases of online exploitation and protect vulnerable users.