A person I know once installed a spying device on my phone which allows him to see all my messages phone calls photos etc... To prevent that I decided to use another device and I find out that the person is still spying on me. The person can access stuff I am sending/recieving (for example on whatsapp) even after I reset the device. I would like to know how he can do that and how to prevent that. PLEASE help. Thank you.