The security data comes from the lock cylinder which is attached to the switch. The lock cylinder and ignition switch both send a signal to the gauge cluster (this is where all the secruity data is processed. They do work together during the start process. So a failed ignition switch can cause that problem. Only thing, after you replace the ignition switch, you may have to perform a relearn, but you can do that at home and it only takes 10 minutes to do.
Actually, you can try that now just to see if the lamp will go off, but it might not due to the switch.
Attempt to start the car, even though it won't. Then release the key and leave it in the ON position for 10 minutes or until the secuirty lamp turns off. After 10 minutes, turn the car off for 5 seconds, then attempt to start again. Watch the light to see if it goes off. Like I said, it might not due to the switch, but it should after the repair.
No, the switch should be available seperatly unless they changed the design.
I have the GM part number, it is 26034119