How can You hack your girl friend's WhatsApp?
Yes I can, it's very easy. I will teach you the social engineering hack
Step 1. You approach your girlfriend, smile and ask, "What is the password for your WhatsApp?"
Step 2. If she answers the question, she is vulnerable to that attack and you are in.
Step 3. If she doesn't answer or gives you the wrong password she is not vulnerable to the attack and you need to ask her, "Can I borrow your smart phone while you are logged on to WhatsApp?"
If she gives you the phone you are in, if not go to step 4.
Step 4. Get a dumber girlfriend.