Is the phraseology in the early portion of the movie The Net realistic?
"Radar contact lost" is standard phraseology.  Most typically it's used when an aircraft far from the radar antenna is no longer being picked up, and it's just an advisory that "we can talk to you but we can't still see you."  (Remote VHF antennas are cheaper &amp; easier to put up in remote places than radar transmitters.)

As for the scenario itself, initial contact with the tower is hardly the point where ATC would first notice that the aircraft wasn't going where it should be.  To get TO the ILS course, you'd typically have Approach Control issuing radar vectors to the aircraft, ending up with "N1234X, 3 miles from Van Nuys, fly heading 100 until established, cleared ILS runway 8 at Burbank."  If the aircraft flies through the course (for whatever reason; it sounds like in the movie the implication is that his navigation equipment has been hacked), they'd issue another vector, cancel his approach clearance &amp; tell him to climb, or whatever.

Also, ATC (i.e. Approach Control, even more so than Tower) will get automated low altitude alerts when an aircraft is below set altitudes.  If an aircraft in radar contact was descending into terrain (and not on final to a runway), well before the radar loses line-of-sight with the aircraft, the controller would issue something along the lines of "N1234X, low altitude alert, check altimeter 30.05, climb and maintain 2000'."

There are non-radar environments where pilot mistakes have put perfectly flyable aircraft into the terrain without any opportunity for ATC intervention.  There have been cases within radar coverage where misread instruments, usually only when combined with an additional pilot error, have put aircraft into terrain or obstacles short of the landing runway.  The smokestacks referenced sounds like a prominent feature well north of Burbank, so at a minimum there's some "artistic license" involved in claiming that a hacked ILS could put the aircraft that far off course in that direction without ATC catching it well in advance of things getting to the point of a crash.

Also, an ILS receiver would be awfully hard to hack, no matter what sort of evil programming genius you are.  You could disable it in several different ways (pair of wire cutters would do that), but the malfunction would be obvious to the pilot early on.  To have the receiver seem perfectly normal but in fact guiding the pilot down too soon would really require broadcasting false signals to the aircraft in real time in a way that an ILS ground station probably can't do -- at least not without triggering a warning in the monitoring equipment that ends up shutting it down.  And even then, when the pilot gets to 200' above the runway elevation, if HE doesn't see the runway lights, he should be going around.

All in all, this scenario has its weaknesses.  The idea that a hacker could create enough problems to bring down a plane is actually more credible now than in 1995, but even so, the most likely problems are a lot less dramatic than what's described -- "hey, where'd all my electronic charts go?"  Aviation has a LOT of safeguards to prevent exactly this sort of scenario from playing out, even with state-sponsored bad guys as the potential threat.

But, it made for a fun movie, so suspension of disbelief and all, right?