Laura said:
Would it be possible for them to shut down the entire internet for everybody except military or government people?
Yes. One way this could be done is through a legal mechanism that would allow them to enter large POPs (points of presence) where the backbones of the Internet converge and literally shut them down. I am pretty sure they already have these legal mechanisms, although I haven't been keeping up on the law. To actually shut down these POPs is actually ridiculously easy. In the states at least, data centers have to have an EPO switch (emergency power off) button located somewhere on-site. It's normally very big and very red and is only a plastic door away from being pushed (in some cases, it's totally exposed). This button exists in case of an electrical accident, pushing it is supposed to disable all power on the data center floor, where all the Internet routers are working. If they do this just in a few places in CA and NY they would almost completely severe the US from the rest of the world via the Internet. Repeat this process across a handful more sites, and anyone not using satellite Internet would not reach non US-sites. Other countries are surely more controlled and maybe one or two sites would need to be shut down to disconnect that country from the rest of the world. On this note, they already flexed this muscle some in Dallas, Texas I think it was about 1 year ago. The FBI powered down an entire data center down because the company was under investigation, effectively shutting down lots of businesses that relied upon their servers being up.
Taking control of the root DNS servers would also do a lot of damage, especially if coupled with packet filtering at all of our national Internet borders. The PTB's already have deep claws into the telco's and service providers, and just blocking port 53 on UDP and TCP would be relatively easy to do and sufficient to stop most people from being able to use international DNS servers. 99% of people won't be able to browse the Internet with DNS down. The feds just need to demand the network engineers at L3 and such hand over the core passwords, then the fed neteng's will lock them out and implement their filtering.
In my opinion, to swiftly and effectively shut the Internet down would require taking physical possession of Internet sites where transit providers such as Level3 and ATT reside. I am thinking some massive and massively intentional virus that "sweeps the nation" and jeopardizes our "national security". The feds will say they are reacting swiftly to the threat as they swoop in via mass raids on the relatively small number of large POPs across the country.
Military and goverment would be unaffected, as they have their own separate networks that they use. I would guess these are separate fiber optic strands (although perhaps in shared bundles with civilian fibers) but that run to dedicated facilities powered separately. These would run between all major military bases and installations, and certainly underground bunkers. Things like SIPRNet: http://en.wikipedia.org/wiki/SIPRNet