ignition switch or security system

That is most likely the ignition switch. The security system would just prevent you from starting the engine and flashing the light. In your case it sounds like one of the switch contacts has failed.

Not real bad to replace. Disconnect the negative battery terminal. Then remove the lower plastic cover under the steering wheel by removing the screws. Now you remove the ignition cylinder by inserting the key, removing the remote key-less entry module and the halo ring around the cylinder. Now you can rotate the key to "on". Then use a punch or nail to push the release tang and remove the cylinder. Now you can go to the other side of the column and use a tamper proof torx to remove the screw that holds the ignition switch and the switch. Unplug it and reverse the process to install the new switch. Be sure to rotate the new switch to the on position before you install the key cylinder.