I'm reading all these reasons why consumer electronics can't be on during takeoffs and landings and one specific reference that is made over and over again is the sensitivity of the ILS equipment. I understand that isn't a Die Hard 2 scenario, but what about simply throwing random interference on those frequencies hoping to disrupt navigation? I know very little about RF or the power levels involved, but a generator inside a hotel room in or around the airport property sounds like a feasible scenario.
There are numerous unclassified papers talking about LOC, GS, MLS and other navaid jamming. There are also instances of that happening, both intentionally and unintentionally. The issue with consumer electronics is made worse is that local consumer electronics on the plane can have local oscillators in the receivers. They are small signals, but they are close to the antenna, hence the greater risk.
Jamming LOC (lateral ILS guidance) and VOR are similar. GS interference is a bit more difficult to provide false readings that make sense to a pilot, when the transmitter is off airport.
The reality is that even GPS can be jammed, faked with stronger signals, etc. Numerous companies make GPS-GNSS simulators, and it is not rocket science to integrate those into jamming systems. Some of the countermeasures are documented in open literature, and other countermeasures and methods are not. GPS jamming becomes an issue with various weapons delivery systems, and creating effective countermeasure packages with limited size-weight and power (SWAP) is a constant challenge.
I concur with @STWilson, that if faced with the possibility of interference, it would be good practice to monitor your approach with GPS, NDB, OM and other navaids. For example, one can always start a timer crossing the OM, even if doing an ILS. Certainly in a war or terrorism situation, additional cross-checks are good investments of effort.
Yes, An ILS could be jammed or disrupted. It is a narrow directional signal emitting from an antenna at the runway. A pilot uses other means of navigation to intercept its signal and verify the legitimacy of its course.
A pilot is trained to cross-check position and to notice irregularities of the ILS indication. She or he is taught to be suspicious of erratic and bogus ILS indications, though this isn't taught in the context of possible sabotage.
Fortunately today, most modern aircraft have GPS, the most robust secondary nav source for an ILS approach, compared to VORs, NDB/LOMs and marker beacons. Pilots will often perform an overlay approach, in lieu of older kinds of approaches, like the ILS . These are so-called because most GPS approaches fly exactly the same path as if the GPS chart is "overlaid" on an older approach chart's path. There are GPS options for most all older approaches. Nevertheless ILS approaches in their original form remain in common use as default option offered by ATC.
Precision (meaning with glidepath guidance) WAAS GPS approaches are becoming the norm with pilots over ILS and other options. An LPV approach is one such example.