My S3 (Jellybean) was suddenly no longer recognised by my PC when plugged in via USB. I solved that by debugging using Developer Options as advised in another thread, which allowed the driver to be installed... again (thank you).

But now if I try to use it as a hot-spot via USB tethering, I'm prompted to enter a network security key.

Previously it just connected without the need for this and furthermore, I don't know where I would find such a key since I didn't set it up in the first place.

Help anyone?