Names and places mentioned herein are hypothetical.

Nimali and Amali are good frieds, they whatsApp each other quite a lot. One day Amali recieved a text message to her mobile which immediately followed by a WhatsApp message from Nimali saying the following
“Hi Amali, I was making a booking at the dentist, Mistakenly I’ve given your number so the pin number came to you. Will you please check your SMS and text me back the 4 digit number?”
Amali didn’t think twice, she checked for the pin number and sent it back to Nimali.
Few hours later Amali wanted to check her WhatsApp messages and to the much of her surprise she couldn’t use her WhatsApp account.
What has happened was someone got hold of Nimali’s phone and checked her WhatsApp. The person installed WhatsApp in his own phone and set the phone number to Amali’s phone number. Then he WhatsApped Amali as Nimali to collect the pin number and entered that pin number in his phone. So Amali got disconnected from her own WhatsApp account

Precaution tips: Carefully check your SMS messages when someone asked for mistakenly sent pin numbers.
Do not respond to those messages unless call and verify with the asking party.