Teenagers are filming crimes including arson and car crime and posting footage on the internet, a BBC Wales investigation has found.
Car thefts and arsons have been filmed and put on the internet
Footage shot in Cardiff by a car thief as he carries out crimes is among clips posted on video sharing site YouTube.
BBC Wales' Week In Week Out programme found other examples of films of crimes being committed placed online.
YouTube said it was a self-policing online community and its rules about content are clear.
Week In Week Out spoke to a Cardiff teenager who repeatedly filmed himself committing a series of crimes and posting the footage online.
In one clip, he gives a running commentary as he and a friend drive around the city in a stolen vehicle at one point stopping to hot-wire the ignition to restart it.
Mobile phone footage taken of a youth stealing a car
In another clip, he laughs as he watches a different stolen car blazing in a field.
He told the programme he carried out the offences because he was bored.
He said: "I've got nothing else to do really, I haven't got a job and I'm not in college.
"There's nothing to do around here and anything that there is to do costs money and no one's got money. We just do it and if anything funny is happening we can look back and laugh."
Other footage found online shows a teenager being attacked on the streets of Cardiff.
Victim James Pilcher, 18, was chased through four lanes of traffic and is then cornered in a garden where he is seen being beaten.
The attack was filmed by a group of youths before uploading it to YouTube under the "entertainment" category.
Mr Pilcher said he did not know it had been filmed until someone told him they had watched the attack on YouTube.
Hundreds have since viewed the footage online as well as people in his own neighbourhood who have been passing clips from phone to phone.
An attack on teenager James Pilcher was put online
Mr Pilcher said: "I feel a bit shown up because everyone in the world can see it.
"It's alright for people who are doing silly stuff like for fun, but when they stick things on there, fighting and stuff like that, it's stupid isn't it."
Criminologist Keith Hayward, who has studied the phenomenon of posting crime footage online, said people doing so were often motivated by gaining notoriety.
Dr Hayward, of the University of Kent, added: "People just don't think there's going to be any consequences when you are shooting this material.
"It's really about technology driving this - you can film it, you can distribute it, you can be your own producer/director, and you can go on YouTube and get your few minutes of fame.
"You can actually re-live these moments, make them available to millions of people."
The US-based site YouTube said it was a self-policing online community and its rules were clear about content.
The footage concerned has since been removed.
Week In Week Out is broadcast on BBC One Wales at 2235 BST on Tuesday.