Non-physical aggression is higher in girls than boys. Boys show open aggression using physical violence and threats, but girls have more aggression (Lilienfeld et. al. 2012).
Girls use an indirect form of aggression marked by spreading rumours, gossiping, social exclusion and nonverbal put-downs (also known as "the silent treatment") for the purposes of social manipulation and bullying. In this day and age of electronic communication devices such as mobile phones, email and internet, cyber-bullying is prevalent amongst girls far more than boys.
Girls create false email accounts with web-based email providers and cyber-bully other girls with derrogatory, insulting, intimidating and gossiping email messages. Since there have been several suicides of young girls caused by cyber-bullying, schools and parents must take this matter very seriously.