2005 Kia Amanti Security part in the ignigtion

I took my car in for an oil change and to get it road ready for a long trip. When the mechanic changed the spark plugs the security light came on and shut the car down. It has been 6 weeks and finally I was told the security part(or whatever it's called) where the key goes into the ignition went bad. What could make this happen? If I had driven that car on my trip I would have been stranded 12 hours away from. There was nothing wrong with the car when I took it in.