Flaming: When two or more people fight online over any issue, using vulgar and foul language, thereby degrading one another.
Hacking: Using a person's device by logging in to his/her account and accessing it without permission. It is similar to breaking into someone's house without permission.
Cyber stalking: Following someone without their knowledge, looking at their pictures, monitoring their activities like where they live, which school they go to, what time they sleep etc.
Denigration: Sending unnecessary information, secrets about someone online, with the purpose of damaging their reputation.
Impersonation: Breaking into someone's account and chatting, posing as that person to his/her friends by assuming their identity. Then person's friends or relatives may not know that it is someone else and may get a bad impression.