I just got done taking a class on security so I'm sorta regurgitating what I learned

. We learned more of the mathematical side of how symmetric and asymmetric encryption works. I'm sure there's some InfoSec brehs around here than can give you a better picture of how it all works.
Something like the DMV would be difficult, but not impossible. All a server is is basically a computer running some software and storing some data. If I can get physical access (read as I can put my hands on the server) then get ready to hold an L because there's nothing you can do to stop me. If you do something silly like use an open WIFI network then

I can easily read the traffic in and out. If I wait long enough then I can find the packets containing login credentials most likely.
With the DMV they'll probably have a setup where the machines with the actual data aren't connected to the internet themselves, but to a local network. Then they'll have machines on that local network that can connect to the data servers and the internet as well. That way there's an extra set of hoops an attacker has to jump through before they get to any data. But everything is for naught if files aren't encrypted. And even if they are encrypted, if the attacker can get a hold of the private key of the organization then they can decrypt those files. Security has to be at every step: files need to be secure, the data location needs to be secure (physically and virtually), the security measures have to be implemented correctly, the programs need to be made smartly.
Everything on the internet uses a server in some form or another, even The Coli. Whether it's privately hosted or hosted using another server, the data is out there somewhere.
I don't know if you know, but the DNC hacks weren't some supercomputer type of shyt. It was done through a phishing attack - fairly easy to do - and that's how the passwords were lifted. That's why you gotta pay attention to the links you click on and the email you receive. It's a scary world out there

.
Side note, fukk the math

. That shyt ain't no joke. Data substitution, maxtrix multiplication, matrix manipulation, XORing shyt. The theory behind AES and how it all works is crazy

.