What is hacking?
Hacking is not necessarily malicious. It's not necessarily about breaking into things.

A hacker is someone who is enthusiastic about tinkering with things and learning how they work. A mechanic could be a hacker. A quilt-maker could be a hacker. A vet could be a hacker (although that would be scary).
[hr]
Regarding your firewall diagram, you write a program to send a network packet via one (or many) of the protocols the firewalls speaks. The packet is malformed in some way to deliberately exploit a bug in the firewall's software, which allows you to change the way that it operates.
Read this: http://altdevblogada...ffer-overflows/

If you don't know of any bugs in the firewall's software that you can exploit, you go to it's login page and type in:
[font="Courier New"]username: admin[/font]
[font="Courier New"]password: admin[/font]
and hope for the best

As for real-life "hackers" who figure out these exploits, they've got their own conference!
[hr]
Before the internet was huge, a lot of effort went into 'hacking' the telephone networks, which people called 'phreaking'.
If you could handle a soldering iron, you could build yourself a small box, which emitted certain tones that would fool the phone system into giving you free telephone calls.

Some of the early equivalents of The Pirate Bay (etc) thrived on the ability to connect to BBS's for free via phreaking.

Another hacking arena is "social engineering" (aka "meat hacking"), which is basically just the art of being a con-artist. Often this can be the most powerful a simplest kind of computer hack -- just trick someone into handing over their password!

What is hacking?

This will vary depending on who you're talking to or what the context is. In general hacking in this context refers to exploiting a flaw in a program. It could be a buffer overrun, it could be SQL injection, it could be a timing issue, it could be exploiting a random number generator's un-randomness....

By using C or C++, I don't seem to see a way that allows your program to go through that firewall. I couldn't imagine how you write your source code that you can hack your way through that weakness.

And once you've reached Room B, what do you do after that?
[/quote]

It depends on the weakness. In the most traditional version, a buffer overflow attack there's a flaw in the firewall about how it uses C style strings (or buffer parsing). You would write a program (or simple script) to send data to the internal host that is malformed so that the firewall tries to read say... 10000 bytes into a 64 byte buffer. Due to the details of how programs work on many systems, code sits next to data. When the bytes are written to the buffer (remember, buffers in C are just pointers) it writes over the bytes after the actual 64 byte buffer. If you send the right data, it will overwrite the firewall's code with the code you sent. That code is usually something like 'open me a command prompt and listen for more instructions'. As the firewall continues running, it then runs that code instead of the code that it should've.

After that it's academic to go where ever you'd like in the DMZ. Firewalls though are pretty bulletproof. Finding a flaw in code on B (that you can legitimately access) is more common these days.

And do you believe the fictitious "hackers" out there capable of doing those amazing things in movies, or books? Do they exist? If yes, tell your story please.
[/quote]

Sneakers is probably the most accurate hacking movie you'll find (mostly because it points out that many exploits are human in nature, not technological). By and large, movies overplay their capabilities and never show what it actually involves because it's boring, tedious work.

Other than using firewalls, movies depicted that hackers can lock out other users, and take the computer as if the hacker owns it in that person's room. Is that possible, taking control of remote computers?

Absolutely. The buffer overflow example I gave should make that clear. Once you've found the exploit, you can run any code that the user running the code with the exploit could run. If the user is root/admin that means removing users, creating users, (un)installing software... anything. SQL injection follows a similar path. You can run any DB commands as the user who's running the software with the exploit.

Other exploits tend to have less impact.

Things that all forms of hacking has in common: It's about 1) having fun; 2) ripping things apart.

Closing this uncomfortable topic now that the OP got his answers.