Security light problems
it stands for vehicle anti theft system, then the light comes on, basically your car thinks it is being stolen (pretty much)
there are a few causes for it:
worn out key/dirty key
broken wires in ign
the above two will usually cause the car not to start, but pretty often my security light will come on while driving.
another cause is a problem with the BCM.. im not too familiar with those problems.. but im guessing it is your cause

