Oh dear fucking Cthulhu, this is like something out of a John Brunner novel: NewsTweak.
TL;DR version: it's a plug computer like SheevaPlug or PogoPlug ... or the rather less benign PlugBot. It runs Linux and has wifi and a bunch of preconfigured software to do interesting things on whatever wifi network it finds itself on. You'll notice it has an extra mains socket on the front, so that it looks like a rather clunky surge suppressor or similar adapter.
In the case of NewsTweak, it uses ARP spoofing to change the text displayed on certain web sites. In the demo video (see that link at the top?) we see NewsTweak changing a headline on the BBC News website. Note that it's not messing with the HTTP transaction, it's doing this at a lower level by injecting ethernet packets into the stream going to the machines running the web browsers.
Next step: they'll add a 3G or 4G phone stage so that it can maintain its own back-channel to Black Hat HQ to receive updated instructions in real time. For example, to look for someone logging onto a banking site or a business application or a government database, and then modify what they can see. Or modify what they can't see, so that an HTML login form pointing at a government server might be silently redirected to a hacker's machine instead, which is running a proxy pointing at the real government server (to enable the hackers to grab the login credentials — a classic man in the middle attack, and the reason why Serious People use two-factor authentication instead of passwords, not that it would help much for this particular session).
Smart organizations (and government departments) treat any wireless network as untrusted for exactly this reason: someone can have added an inconspicuous wall-wart loaded with penetration tools to your network, and it could be listening in on everything your users type.
Moral of story: if you can't see the wires you can't trust the channel.
This sort of gadget is, in bulk, extremely cheap — I bet you could order them for well under $100 in batches of a thousand and up. Say you're a repressive regime, but not so repressive that you can just haul random dissidents off to the torture chamber without paying lip service to due process. How hard would it be to plant these things in your targets' homes, so that you can gaslight them by interfering with the news they're reading? Call it a digital agent provocateur. Say you're the DHS and you want a steady stream of clueless Al Qaida wannabes to arrest and show on CNN to keep everyone afraid enough to go along with your PATRIOT Act extension? Plant these in the homes of young muslim males who hang out at the wrong mosques, crank up the volume of hateful news, and see who snaps ...