To the actual issue, i wonder how practical this is? In that i mean what level of power output is required to override the correct signal and at what distance? Is this something that could be a real issue, impractical? What?
When gauging the newsworthy-ness of a problem, the scope of its impact is always one of the first factors that journalists consider.
The scientists who conducted the experiment — done with permission of the yacht’s owners — say their ability to broadcast counterfeit GPS signals that triggered no alarms within the ship’s navigation system highlights a serious flaw in transportation networks on land and sea. Some 90 percent of the world’s freight moves by sea.
Let's say a captain enters a course to stay 500nm offshore of a pirate-infested coast (btw, after Somalia, West Africa is now a pirate hotspot[1]). By interfering with the GPS, the ship could be turned imperceptibly towards shore, and after a day be within range of pirate boats. The GPS display on the electronic charts would still show the intended course, because the GPS thinks it's on the right track. And without any land for reference, the captain or crew might not notice. If GPS is the sole position-finder, the fake coordinates would also endanger the reliability of ship-to-ship collision detection such as AIS[2].
With a cell phone or any consumer device, the user has to constantly read the GPS output and then react to it based on the roads or other physical landmarks. You couldn't just "steer" a person to the wrong place by making the GPS believe it's in a different location. And then I can't think of any other "exploit" that you could do with the GPS on a phone.
As mentioned elsewhere in this thread, the solution to the boat navigation problem is to have alternate sources of position info (Loran, GLONASS, etc.). Alternatively, the error introduced by the fake GPS could also be detected by weather info. Any deviation from the dead-reckoning course (heading and speed) can only be accounted for by wind and current. I believe wind and current forecasts are fairly common for all areas of the globe now, so the calculated values could be compared to the expected values and raise an alarm if they are far off.
[1] http://gcaptain.com/tag/piracy/ [2] http://en.wikipedia.org/wiki/Automatic_Identification_System
First, the fact that expensive machines can be brought down by cheap components is still interesting. Nobody will really care if your $80 cell phone can be spoofed.
Second, GPS receivers are not all the same. There are many different techniques you can use to make your receiver more resilient against spoofing, from cheap and easy things like adding Galileo and GLONASS support to crazy expensive things like adding backup star tracking and inertial navigation systems to cross-check the GPS results.
At the least, one would expect such an expensive ship to cross-check GPS results with internal dead reckoning to reject obviously bad GPS coordinates. That it didn't do this suggests that shipbuilders (or, at least, buyers) aren't aware of the spoofability of GPS. Articles like this make people aware of the problem and its solutions, solutions which simply don't apply to an $80 cell phone.
I guess it has more to do with the fact that unless you have a great Kalmann filter design, your IMU will likely drift off course rather rapidly, whereas GPS spoofing wasn't as easy or as popular as it is today (and I would say it really isn't that popular outside of major areas today, as it stands). Either way, you're right, the GPS coordinates should definitely be checked against the internal dead-reckoning. However, then you have to ask yourself how you know the internal dead-reckoning is still on course. It's a tricky problem, and hopefully the solution doesn't just tend towards "add more sensors."
EDIT: changed an "isn't" to "wasn't"
If I were designing such a system (and I'm sure I've overlooked about a million subtleties), I imagine I would make it so that the GPS corrects the IMU for small perturbations that lie roughly within the IMU's predicted error budget, and that the IMU causes the GPS to be ignored if the GPS coordinates suddenly diverge greatly.
In other words, the IMU is going to be saying something like, "our position is X, to within 5km". If the GPS disagrees with X by 1km or perhaps even 10km, correct the IMU's current state using the GPS. If the GPS disagrees with X by 100km, ignore the GPS until it gets its act together.
Seems like a decent first pass, at least.