A soldier has admitted grooming a child after sending explicit messages over the internet from his Army barracks.
Winchester Crown Court heard 25-year-old Craftsman Sam Dallow from Birmingham thought he was contacting a 14-year-old girl.
In fact it was self-styled paedophile hunter Shane Brannigan, who handed Wiltshire-based Dallow to the police.
A senior police officer warned against vigilante action – saying it risks jeopardising ongoing investigations.
Dallow, of 6th Battalion The Royal Electrical and Mechanical Engineers, based at Tidworth, admitted attempting to meet a child following sexual grooming.
The sting was carried out at Andover train station on 11 April where he was greeted by Mr Brannigan and a colleague who filmed their exchange.
The footage and online exchanges were given to Hampshire Police.
The vigilantes claim they are helping budget-stretched police forces.
Mr Brannigan told the BBC: “Saying and crying they’ve got no money, no resources, no funding, there isn’t enough people in the team to do this sort of thing.
“Leave it to people like me who actually care about the investigation.”
Police forces have warned that amateur detectives can jeopardise ongoing investigations.
The national policing lead on child abuse investigations, Chief Constable Simon Bailey, said: “They are taking risks they don’t understand.
“Revealing the identity of suspected paedophiles gives the suspect the opportunity to destroy evidence before the police can investigate them.”
He added that the risks of wrongly accusing people in a public forum can also have serious consequences as the public often assume they are guilty.
Sentencing takes place on 8 June and the judge has warned Dallow may face time in prison.
The Army told the BBC it is considering whether to take any further action after sentencing.