I am not a lawyer, but I sometimes behave like one; therefore I appear here today in order to give the Unix(tm) community some free legal advice on a problem which most people don't handle correctly. Say you're trying to connect to another computer, and just as you get to the login prompt, you realize that you've made a mistake and have connected to a computer that you never saw before. At this point you are in a very delicate legal situation. You have used up some CPU time from the unknown computer because it had to print the login prompt for you. Also, while you are trying to decide what to do, you may be preventing legitimate users from logging in. Now you must carefully demonstrate that what you have done was unintentional; otherwise you will be in DEEP LEGAL TROUBLE.
I would like to pause for a moment and ask that small group of people at the back of the room who read too much fantasy to please stop chanting "innocent until proven guilty." Your naivete is very irritating. If you don't quiet down, these nice policemen with the electric cattle prods will escort you to the alley behind the building and will try to explain to you why you are wrong.
OK, that's better. So, as I was saying, you must clearly establish intent when confronted by that login prompt. Now most people would type ^D and be done with it, but that is in fact the ABSOLUTELY WORST thing you can do. In Unix(tm), ^D signifies end of input, but it also signifies that you are satisfied with what you have previously typed! Thus by typing ^D, you have openly admitted that your attempt to access the computer was intentional, and that you are just taking a break to celebrate your success so far.
To ensure that you are recognized as being innocent, you should type ^C to the login prompt, because as we know, ^C means that what you have typed before was wrong. When you type ^C, nothing will appear to happen, but actually the computer will be notifying the appropriate authorities. What you should then do is slowly move your hands away from the keyboard and wait for them to come and take you away. And whatever you do, don't make any sudden moves with your fingers. As I said, you aren't guilty if you type ^C, but the authorities like to check anyway, just to make sure. So you will have to explain what you have done over and over to people who wear watches that are one hour early during daylight savings time (and I don't even want to speculate on what their VCRs at home are doing). You will have to explain to them why your computer made the wrong connection even though computers don't make mistakes, and why the control key can't be released before pressing the C key, and why the C in ^C is uppercase. They will not have a reason to find you guilty if you carefully suppress any coughing, especially dry coughs. Also, don't even mention your job if it entails dull writing or driving horse-drawn carriages. And just to be safe, don't let them get your hackles up and don't use any hackneyed phrases. Once they have grudgingly accepted that you are probably not guilty, you can ask if they will give you back your computer and printer and half-empty can of Coke(tm) that were seized as evidence.
Certainly ^C is a legally-correct response to a Unix(tm) computer, but as we have seen, it may not be a very good response. Besides provoking suspicion by looking like two characters instead of one, ^C may in fact be completely inappropriate if the machine that you have mistakenly connected to isn't running Unix(tm). Since you could have connected to any sort of machine, you don't really know if the login program of the machine will be able to deal with control characters without crashing and letting you into the system. Therefore, the law allows you to type ^C to an unknown computer only if you know the computer.
The best legally-correct response to the mistaken login prompt is to press the caps lock key down and type a certain single sentence of 666 words to both the login and password prompts. However, due to the possibility of making a mistake when typing the sentence to the password prompt (and thus completely nullifying its effect), most people prefer the officially-standardized exit string, "give up, end, stop, terminate," which was proposed after years of deliberation by a standards committee that unfortunately does not yet have a name -- a minor detail that the members are still working on and hope to specify soon.
Most people prefer to go one step further, and only type the acronym of the officially-standardized exit string to both the login and password prompts. And if that acronym doesn't work, feel free to try some other acronyms.