To see if your WiFi is being stolen
Do you notice that the Internet slows you down? Does
the connection drop?
Did your operator
tell you that it wasn't their fault? To check which devices are connected to
your router, you can use Fing: this program will tell you in real time which
devices are connected to your network. If you see one that is not yours
(neither your PC, nor your mobile, nor your Smart TV ...), then you already
have reason to suspect that someone is taking advantage of your connection.