1.Easy to waste a lot of time on the internet. You can start surfing, and then realize far more time has passed than you realized. Internet and television together of added to the more sedentary lifestyles of people which further exacerbates the obesity problem..
2.Children are becoming  couch potatoes.
3.Spending lot of time online creates stress.
4.It creates mental sickness.
5.People get addicted to internet.
6.Though it has loads of useful informations,it has bad and unwanted informations that affects the children.
7.Hackers can use internet for identity theft
There are many causes on Internet usage. Some of them are:-
1. Due to Internet charge we can easily waste the money.2. We can't concentrate on studies.
3. Instead of spending time on Internet we can read books.
4. Because of many social networks children are been spoiled.
5. We can use the Internet when we have projects,home tasks,seminars..........etc.