This is another VAT site, that actually goes in to bypassing the system.
I know on my vehicle, the blinking security light indicates that no resistance is read on the key, biggest offender is wires broken in the ignition cylinder. When this happened on my car, I turned the ignition key, electronics fired up, hit the key to start, and nothing happened. Then I looked at the dash, and saw the blinking security light as you described. One VATS bypass later, I was back in business.