A Northampton school has issued a warning to its pupils about using a popular music video app - after national reports of paedophiles using its messaging system.
The free-to-purchase Musical.ly app allows users to create 15-second lip-synced videos and share them.
But parents across the UK have aired concerns their children have been asked to send naked pictures of themselves to anonymous users within the app.
Police in the UK are known to have investigated claims of inappropriate messages being sent to children on the app.
And this week Hardingstone Academy sent out letters to parents warning them to be vigilant.
The circular, signed by principal Zoe McIntyre, reads: "It has been brought to our attention via Northamptonshire Safeguarding that there has been some inappropriate activity taking place on the online app Musical.ly.
"It is important you speak to your children about who they are having conversations with when using the app, or apps of a similar nature.
"Children must only speak to friends that they know and they see face-to-face.
"If they don't see then face to face they are then classed as a stranger."
The letter goes on to say the school is taking steps to educate children on the dangers of using the internet, but it states it is not possible to monitor all of their online activity.
If a child has been contacted inappropriately, the letter concludes, parents should contact Northamptonshire Police on 101.
Musical.ly's website states parents should monitor their children's activity on the app.
It states: "Keep track of what they post and who they are communicating with and talk to them about basic internet safety. "
A spokesman for the US firm told The Mirror last year: "Musical.ly prioritises the safety of our users and strives to ensure that all musical.ly users can enjoy our application without abuse or threats from any other user.
"We take appropriate measures to expeditiously remove offensive or inappropriate content from the musical.ly app."
Northampton Safeguarding Children Board has been contacted for a comment.