Why do many public * * * free WiFi users log in with their mobile phone numbers and SMS verification codes?

This is what they set up on the router, and they need to be bound before they can log in. If you use wifi in banks, cafes, fast food restaurants and other environments. Just ask the clerk directly. No big deal. You can also use your laptop to crack the wireless wifi, but I advise you to give it up. It takes time and effort.