Hardware trojans

[ManOfSteel]

In a lot of movies and series we keep on seeing hardware trojans. Since hardware firewalls are possible, hardware trojans should also be possible, right? How do you think they work or could work?

[rwfromxenon]

Well, you see, you build a giant wooden rabbit. Then Gallahad, Launcelot and I wait until the enemy is sleeping, and jump out and kill them unawares.

[CESS.tk]

And I thought Brad Pitt and Orlando Bloom had something to do with it...