While it's a bit tinfoil hat, it's not impossible that there could be hardware backdoors in processors or other hardware triggered by a very specific sequences of packets.
What would be hard is also making sure that packet sniffers in the middle wouldn't be able to detect it. Specially with all the varieties of router hardware. Are we going to have a backdoor in all of them that prevents passing on that data?
And you know, given the tens of thousands of people involved in chip design, are we to think that absolutely no one, anywhere, would've leaked that there was some anomalous circuitry in the chip designs which they were told not to worry about it?
