You can hack into anyone’s account without their knowledge by using Cocospy. Learn a lot more about Facebook messenger hacking via cocospy.com/blog/facebook-messenger-hack.html . There might probably be many apps but as I have used it on my own that’s why according to my experience I can tell that this is one of the best apps available in the market these days. Just add the iCloud account details of the targeted account’s phone and that’s all you have to do. Within a couple of minutes, you would be able to gain access to the account without the knowledge of that person.