Arinc 629 is B777 (and A330/340)? and yes it's linked to a standard TCP/IP network (this is where the "hacker" is), but it's one way communication.
Yes it is 777/A330/A340. It is not Ethernet, it is not simplex, it is time division multiplex (multiple source, multiple sink), with a limit of 128 devices per bus. Inductive coupling is also used by design.
My summary of a/c hacking stories so far is this: There is a wire from the headphone socket on seat 29C which is connected to [insert something here] which again is connected to a wire via [insert box here], and through various other devices, I have now, very ingeniously, traced physical wires/"connections" from the headphone socket to the FMS. They're physically connected, it must mean something can be hacked, because it's computers! Yet if I plug my [insert evil hacking tool here] into the headphone socket I have no control over the FMS, despite the "physical connection".
He is talking about connecting his PC to the IFE network by cable.
I'm not sure how layered or embedded aircraft systems are, but in the world of commercial systems the application layer is often riddled with holes. I'd imagine that on an aircraft the systems are very embedded.
The boxes under the seats are essentially disk-less single board computers running windows or linux connected to a windows/linux server. They boot off the server with bootp or similar. The kernel versions I have seen boot are very old.
Lots of these under seat boxes are available, even complete IFE racks. Many of these early generation IFE systems and seats have already been scrapped by airlines, and anyone can buy a seat, IFE rack, or even a full fuselage from a scrapper for the right price.