The US stealth drone was captured by Iran spoofing its GPS coordinates tricking the bird to land within the Iranian territory instead of it's actual programmed landing zone, Afghanistan. Iranian engineers, only a few months back, claimed that the drone’s GPS was reconfigured which made it land inside Iran.
According to the US officials, RQ in its name means that it is unarmed and some industry experts who have written about the Sentinel stealth is that its design makes it more of an operational platform not an intelligence gathering aircraft. It was used to fly support during the Bin Laden raid. However, according to the Iranian news, the drone was shot down and recovered almost completely intact which goes as a warning to the US.
According to an unnamed Iranian engineer who has been working on the US bat-wing RQ-170 Sentinel, the spoofing method used allowed the Iranians to divert the landing of the bird without even hacking into the remote-control signals of the US control centre.
The GPS weakness of aircraft has been a concern for US since a long time. Such an attack is much more sophisticated than ECM jamming due to being executed under cover and finding out the hacker is not possible until the spoofing has already been done. The attack method allows the GPS receiver to send wrong GPS signals which makes the drone believe that it is located somewhere in space while it is flying at its normal altitude, making it to reduce altitude and actually land. The US officials lay the claim of their loss of the stealth drone on a supposed malfunction from their end.
The Iranian engineer, however, claims the GPS navigation to be the weakest point. After being “jammed” by sending noise over the normal communications, the bird automatically goes into autopilot mode and doesn’t know what to do next. It can then be tricked and commanded into doing whatever the controller wants.
None of the current GPS systems are “spoof proof” due to several reasons. The main reason being the near impossibility to validate consistently on a “one way” communications channel because of “replay attacks”. Therefore all the GPS sytems require an additional channel that is not possible to jam.
Claims have also been made that Iran has sold the stealth to China so that China may undertake serious investigations on the other hand Pakistan is also believed to have shared with China, the stealth technology from the stealth helicopter that crashed in Abbottabad attack.