Background: traction control requires detecting wheel spin (wheels turning faster than the car is moving), and then reducing power to get the wheels to slow down and grip again. Power reduction can be done by changing spark timing or even dropping spark. Wheelspin detection usually requires comparing the speed of the driven wheels vs the undriven wheels, and triggering whenever the delta is too large.
The F1 rules prohibited traction control, so no undriven wheel sensor was allowed. How then can you detect wheelspin?
Well the F1 car has this big ol' airbox and there is a sensor in the airbox that detects airbox pressure (as part of the engine control unit control strategy) What Ferrari realized was that the airbox was a pitot tube and so provided an indicator of forward airspeed.
So the spark maps were altered so that when airbox pressures indicated a certain airspeed, but engine RPM and transmission gear indicated a different speed, spark timing was retarded to lower power.
The brilliance of this was that there is nothing illegal going on — spark maps are free to be whatever. It's just the engine calibration.