Microsoft.com - Microsoft has a nice text based walkthrough of this.
Digg.com - The story on digg. this page.

Box 1: What this does is short out the two lines, ring and tip. No electrical flow into the house, no dial tone. The line will work if someone connects anywhere on the "phone company" side of the box.

Box 2 (classic): This is the oldest and the best way. It sends ~9 volts into the phone line. Since "talking" voltage is ~10 volts it basically says "hey, someone is on the line". No matter where you try to hook up, this line should be busy.

Box 3: Same idea as Box 1, but a little more subtle. However this way, if a phone man hooks up at the box outside, he won't see a wire connecting the two prongs. He will hook up at the box outside, and get dial tone. The only thing he would be able to tell them is "Try un-hooking all the phones in your house one by one. One of the phones probably has a short, and that is ,most likely, the problem." Or he would just say, "It's an inside wiring problem, and your service plan doesn't cover this. I can continue, but it'll cost $80 for the first two hours, and $40 every hour after that."

Fedora Redhat - Fedora Redhat can be found on this page.
Run levels overview - A nice overview of run levels can be found on this page.

I'm just going to use a very simple/generic line of SQL to explain:

SELECT loginID FROM user_table WHERE (userName='$userName' AND Password='$Password');

This is grabbing the loginID from the table "user_table" as long as the username, and password match.

Now, take the injection: hola' or 1=1--

Note: "--" is a single line comment, it basically tells the interpreter, "Forget about the rest of this crap."

So here is the line of code as read by the interpreter:

SELECT loginID FROM user_table WHERE (userName='hola' or 1=1--' AND Password='$Password');

Obviously the username isn't hola, and even if it is... it doesn't matter. It's the "or 1=1" that we're interested in. It's saying "Grab loginID from user_table where the username is hola, or if 1=1." Since 1 always equals 1, it grabs the first loginID from the top of the table. And since you added the comment, it ignores the rest of that line, and follows the rest of the script to log you in.

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