ADS-B Hard to Jam
Like cell phones, ADS can be disrupted by jamming in interactive mode.
On the other hand, in one-way broadcast mode, ADS-B only transmits without waiting to receive any signals.
To jam the transmitted ADS-B signal, a jammer would need to generate and radiate a conflicting signal at the same or greater effective power as seen from a land-based receiver. This is difficult to do without a specialized antenna mounted outside the metal fuselage.
It is not entirely clear at present whether ADS-B transmissions from MH370 were actually disabled, or whether they were merely not received due to range issues. FR24 appeared to say that they lost the signal as the aircraft disappeared below the horizon.