NSPCC says smartphone apps increase bullying and abuse
The NSPCC says smartphone apps are making it easier than ever before for people to be bullied and abused online.
The children's charity is worried about ones that let strangers talk to children, pinpoint their location and send explicit images.
It is also warning that blackmail through pictures and videos is becoming increasingly common.
Senior police officers at the Child Exploitation Online Protection centre (Ceop) agree.
Peter Davies is the UK's most senior child protection officer.
He said: "One of the operations we completed last year was two men in Kuwait, purely online, abusing and blackmailing children, particularly girls, in the UK and around the world, dozens of them.
"The level of harm was immense and life threatening."
Things didn't get that bad for Sophie Thorne, who's 17 and from Swindon, but she was bullied through a smartphone app for several months in 2012.
She said: "At first it was just name calling and then it got really personal.
"[Things like], 'I know when you're at home, I know when you're alone.' Then it got to death threats.
"When I got a notification on my phone it beeps until you read it. Then another one would come through so it was just never ending really.
"I felt quite alone because I'd never really been through anything like this before and I did start self-harming towards the end of it."
Many people say the easiest, quickest and most simple way to stop this type of bullying and abuse is to switch the smartphone off.
"Just saying turn it off doesn't work," according to Mr Davies.
"For a lot of people internet access in their pocket is an integral part of their life and it's how they keep in touch with their friends."
There are of course many thousands of apps that cause no problems at all.
Many people also use the ones the NSPCC is worried about without any problem.
When it comes to numbers Claire Lilley from the NSPCC says it's nearly impossible to know just how many people are victims of smartphone bullying and abuse.
"It's really difficult to put a figure on it," she said.
"Because the technology is moving so fast, as soon as you gather the figures they're out of date because the technology's moved on."