A study published in the Journal of School Health suggests that 72% of youth have been bullied online in the past year, and most of them said that they would not tell a parent about it. Although the internet provides a degree of anonymity for bullies, the majority of their victims knew the perpetrator or believed that the bully was a peer from school. Kids who were bullied at school were far more likely to be bullied online, and they tended to retaliate at school. The researchers concluded that there are more similarities than differences between real-world and cyber-bullying.
You can read the complete study here.