You probably already know and have used the “last seen feature” from WhatsAapp, which lets you know when was the last time that a contact from your list has read the messages you send to them. The feature also shows you if a contact is online or not. You can opt-out of this tracking activity from your phone if you go to Settings, select Privacy and disable the Last Seen option.

However, a software engineer made an experiment explaining how you can still track your contacts even if they hide WhatsApp Last Seen option.

Using a laptop, a Chrome extension and WhatsApp web, Robert Heaton has managed to crack the Last Seen of a WhatsApp contact through a Javascript code – mainly decoding a protocol WhatsApp uses. With this trick, you can see the entire WhatsApp activity of a contact, if he/she is online or offline. And if you want even more details, you can connect the data from WhatsApp with the info from Facebook and see what the contact posts on the social media platform. What’s even more interesting is that you can track your targets even if they don’t have you on their contact list.

Basically, this is a flaw from WhatsApp that could help many online snoopers track your activity much easier.