There is an advanced check-point on the road leading up to Atatürk airport. Problem is, as with many things in Turkey, that it's mainly there for show. I've lost count of how many times I've passed that security check-point, but it's in the double dozens, and I've never, ever, been anything than waved through - often without so much as a quick glance inside the vehicle. Whether arriving by taxi or private car made no difference.
Then there's the security check at the doors leading into the terminal. Manned by staff who visibly don't give a toss, and/or haven't a clue how to operate a scanner, and/or wouldn't know what bomb looked like on an x-ray if their lives depended on it.
In short, IST has a lot of 'security', trouble is that it's about as much use as a chocolate fireguard.