What does the security light on the dashboard mean?

Replace the key cylinder. It suffers from a design flaw in which the detent plunger inside the locking mechanism will fail to hold the key in the operators desired position when it's spring becomes weak. There was a class action lawsuit against GM years ago about this problem due to it resulting in fatalities. You could just replace the detent plunger with the more updated longer one, but chances are by that time the key cylinder is worn out anyway. The new cylinder should come with the new updated detent plunger.

After replacing the components, the computer will need to "re-learn" the anti theft system. The procedure to do this is simple and takes 30 minutes. I recommend hooking a battery charger to the battery while doing this because it will not be successful if the battery charge level drops too low.

Turn the key to the on position, and wait 10 minutes. The security light will flash continuously during that time and will stop afterward. Then key off and key on again. Repeat this step twice for a total of three 10 minute cycles. Then the car should start and run as normal.

Note: The new key cylinder will come with new keys as well, so you will have two different keys for your car as you will need your original keys to lock and unlock your doors. If this is an inconvenience for you, take your original key and new key cylinder to a locksmith and they should be able to pair your new key cylinder to your original key.

Good luck.

Make a service appointment to have the recall work done, and have the service manager explain everything.

Yes, related. And try not having 100 pounds of keys and stuff hanging from the key.