More than one in four secondary school kids say they've been a victim of cyberbullying, according to a new survey.
The charity Beatbullying's study for Safer Internet Day spoke to 4,605 young people aged 11-16 across the UK.
28% said they'd been bullied over the internet or a mobile phone.
One in 13 said they had been threatened repeatedly - suggesting that as many as 350,000 secondary school pupils have experienced constant cyberbullying.
Victims found the cyberbullying left them wanting to avoid school, suffering from lower confidence, and living in fear of their safety.
But it's not just children who are victims of cyberbullying - one in ten teachers say they've been harassed too.
Beatbullying is calling for internet and mobile companies to do more to support children and young people.
Have you been bullied online?
The best thing to do if you're being bullied, whether online or not, is to tell your parents or guardian, or someone you trust - and talk about it.
We want to hear about your experiences. Have you ever been cyberbullied, and if so, what happened? How did you get things sorted out?
"If I was cyberbullied I know I would tell somebody. My teacher told me sometimes you can even phone the police."
Mitchell, 8, Glasgow, Scotland
"Thankfully I've never been cyberbullied but do still have concerns. I tend to avoid ever accepting a friend request online and I don't go to sites my friends recommend if I don't know them."
Chloe, 11, Leicestershire, England
"Numerous people get bullied every year. Bullies are just cowards deep down!"
Priyanka, 10, London, England
"I have never been cyberbullied and this is because I don't have Facebook etc."
Thanisha, 11, London, England
"I have never been cyberbullied before but my friend has. I was the only one who knew about it so I decided that I should tell our teacher and he solved it. I think people have to take action. Cyberbullying has to stop!"
Rebekah, 10, England
"I think cyberbullying is horrible. I was once bullied on Facebook. One day a bunch of boys were really nasty to me and I was friends with these boys. I was left sad, confused and really disorientated."
Ricky, 11, Pontypridd, Wales
"I was cyberbullied along with my mates last year. I was too scared to tell my mum and dad so I told my teacher and they got the Head involved. She reported him to CEOPS, it's all OK now though."
Jiorji, 11, Manchester, England
"I have been cyberbullied before on an online girls' game site. I reported them and they were banned from the site. I think it's sad that people do that. I don't see what the point is, it's mean and hurtful."
Anna, 13, Pittsburgh, USA
"I think cyberbullying is really wrong and it's very hard to talk about."
Maisie, 10, Leicester, England
"I was cyberbullied when I was nine - it was so awful and it was even on my BIRTHDAY!"
Martin, 14, Leeds, England
"I've never been cyberbullied but I think people who do it should feel very bad because it's nasty, horrible and sad."
Rachael, 10, West Yorkshire, England
"I was cyberbullied last year and it's very hard to deal with. It was getting so bad I told my mum and my teachers and it was sorted out. Now everything is fine and I'm happy that I told someone."
Jade, 11, Liverpool, England
"I have been cyberbullied, but luckily my mum saw it and reported it. We then rang the police so they could be warned that the person doing it was a bully. I didn't like being bullied and neither do other people, so it needs to stop!"
Takanna, 10, Lancashire, England
"The worst cases are when you feel really hurt or intimidated by a comment, but when you try and tell someone they don't understand you."
Elena, 13, La Hulpe, Belgium
"I was cyberbullied when I was nine. People kept sending me nasty massages over an online kids' game. I got really annoyed and ended up reporting the bullies."
Thomas, 11, Scotland
"I think that those horrible people who cyberbully are mean and nasty, and they should get a life and stop making people's lives a misery!"
Holly, 11, Derbyshire, England
"Cyberbullies need to understand that it upsets the victim and they need to imagine themselves in their position. I can't imagine why someone would do that instead of being mature and talking to them."
Aliya, 11, Northampton, England
"I've been cyberbullied once or twice before. It's just these horrible girls/boys who think they're better and stronger than you. They only do it because they're jealous. Act like it doesn't affect you (even if it does) because then they won't get what they're asking for! And make sure you tell a trusted adult and then tell the school. When this was happening to me, my school sorted it out instantly. I don't think those girls will be bullying me again any time soon!"
Olivia, 12, Plymouth, England
"I think cyberbullying is really wrong. I think that talking about it in lots of places helps to stop it because it encourages people to think about how bad it is."
Isabelle, 9, Cambridge, England
"Luckily, I have never been cyberbullied but I know someone who has. They told me they felt desperate, scared and helpless. We told her mum and it was all dealt with, but the cyberbullies are still always mean to her."
Emz, 13, Darlington, England
"Cyberbullying is horrible and people who do it should think, 'What if it happens to me - how would I feel?'"
Ulysse, 9, Derby, England
"I hate cyberbullying, it happens to me and it's just sad. The people that do it must have sad lives."
Chloe, 12, Rochdale, England
"I was cyberbullied when I was 11. It was horrible and people who bully people should think again before saying horrible, nasty things and think how they would feel if it was them being bullied. Every type of bullying should stop - no one deserves to be bullied!
Hannah, 13, Preston, England
"I have not been cyberbullied but I think the people who cyberbully are horrible and make other people feel blue and upset."
Joseph, 8, West Sussex, England
"When I was bullied I told my mum and dad - that was the right thing to do."
Wesley, 11, York, England
"I have been bullied online so reported them and they got told off. It is wrong to bully and best reported."
Rhiannon, 9, Northumberland, England
"I have been cyberbullied. It's horrible, it was mostly about how I look and it made me feel horrible about myself."
Kira, 11, Manchester, England
"I try to stay away from sites that could lead to cyberbullying. I know people who have been cyberbullied and it can be really depressing."
Elena, 13, Belgium
"I got cyberbullied on Facebook. I had lots of nasty and vicious things posted on my Facebook page and a lot of people started doing it. In the end I deleted my Facebook and confronted the bullies."
Katie, 13, Sheffield, England
"When I was younger I was cyberbullied and sometimes still am. I feel people could do more to stop this behaviour because it's lowering self-esteem."
Hayley, 14, Powys, Wales
"Once, on a multi-player game. I was on a public server and a gang of friends called me names and swore at me. I felt upset, sad and confused. I didn't know why they were doing it! But after a day of talking to them they said sorry. But I'm not sure they meant it and I still don't feel safe around them."
Louis, 11, Wiltshire, England
"I have been cyberbullied. It's just sad to think that the bully is harming a young girl."
Chloe, 12, Derbyshire, England
"I have never been cyberbullied but I know some people who have and it needs to stop!"
Skylar, 12, Ohio, USA
"No I have never been bullied online, thankfully."
Emily, 14, Bridgend, Wales
"No I have not been cyberbullied, but I think it's just sad and wrong."
Rosie, 14, Bridgend, Wales