More than a quarter of girls in the UK have been picked on by email, the internet or mobile phone, according to a new survey.
The study by Girlguiding UK looked at girls as young as 10, and found 28% of them had problems with cyber bullying.
The organisation has made a new guide which says girls shouldn't ignore the problem, but learn to handle it.
It also advises keeping things like your mobile phone number, email address and online profile information private.
Tips on avoiding cyber bullying
Don't respond to nasty texts or emails
Save any nasty texts and emails to show adults
Report cyber bullying
Keep passwords safe
Don't give out personal details online
The guide also talks about the skills you need to be a good friend.
Denise King, head of Girlguiding UK said adults could learn about friendship skills too.
She added they were "important not just when you are young but throughout your life."