To use 'prone' mean easily done. The early generation of radar guided missiles were indeed prone to jamming, but so were the early generation of IR guided missiles as well where there were plenty of stories where the IR missile should not be launched when the enemy is flying into the sun. That is not the case today for both guidance methods. Radar guidance is superior to IR for target resolutions: speed, heading, altitude, and aspect angle. All of those are direct results of the medium -- EM waves. For IR guidance, we have only general direction and intensity, Any other target resolutions must be contrived, meaning interpreted from alternate means. So while this seemingly make IR guidance more vulnerable to deception/distraction tactics, the shorter range involved in using IR missile with today's sophisticated sensor and data processing make the target the more vulnerable one. It is a seesaw where counter-measures will have the upper hand at one point, then the sensor-guidance will take back the advantage at another point.