lost a drone that was last accounted for more than a hundred miles inside the Iranian border. What is up for speculation, however is the manner of the drone's coming to ground.
At the moment, the US is claiming a malfunction while the Iranians are claiming that they forced it to to ground electronically (after claiming to have shot it down, of course). Given that neither side has managed to pick a story and stick with it, I think that it is not unreasonable to just say that they have our aircraft and are not planning on giving it back.
That being said, the American drone program has had a number of security issues in the recent past. Furthermore, electronic attacks of this nature have been discussed for more than a decade, first coming to prominence in 1999's Unrestricted Warfare. Even if Iran did not actually carry out an electronic attack against a US drone, this remains the most practical type of defense for a less-than-super-power. Anyone can buy a device that can block cell phone signals online for less than $30.00 or even make one for cheaper, assuming that you have access to the right soldering equipment (or buy it here). From there, it is just a matter of increasing the range and honing in on the correct frequencies to block.
Though I sincerely hope that we are using technology more sophisticated than cellular signals to control our drones, waves are waves and have weakness as such. As the use of drones becomes more prevalent worldwide, the value of this type of relatively unsophisticated electronic blocking will become more relevant and likely more widespread. While I am sure that there are those with a significantly greater understanding of these matters than I that are working on this issue, this might be the biggest potential chink in the US's technologically superior armor.