How do I convince my parents to let me get a Facebook account?

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My dad thinks that if I'm Facebook, the computer will get viruses an then we'll have to get a new cmputer. My mom thinks it is a waste of time. But I want to be able to talk to my friends over the summer. How do I convinve them getting a Facebook account is a good idea?

Also, if I make an account my parents don't know about, my family who does have an account will probably tell my parents, then I'll be in trouble.