Some of you are making arguments based on ridiculously improbable occurrences. To hack or phish with a 360 you must physically modify the machine. That means cracking open the hood, and then installing new components, or removing old components. These things are not going to happen if a friend happens to come over, and if you barge in on a friend that is ripping apart your console you need to stop being that persons friend right away.
Speaking to those that lend consoles you already have the option to disable their access to Live on your machine. You can disable numbers of features on your console so they cannot do something that you do not wish them to do. Even if you choose not to. How are you a innocent victim. You are the one who is taking a risk. How many people lend their friends credit cards. Not many of us would do that no matter how much we trust our friends.
Anyway if this happens and they get caught doing something like this on your machine. You have a couple options first you should probably expect restitution, and if that is not forthcoming you have legal rights to either file criminal or civil charges. Remember hacking and phishing are real crimes. That your pal can go to jail for, and posing nude on unsecured networks that are visited by children is also a pretty heinous crime in most places.
Your also pretty good in the second hand market as long as you avoid peer to peer transaction, and frankly you should already know that is dangerous. A unusable machine can be returned to the store, and they can file the criminal charges. In fact it is pretty stupid to sell a console that has been illegally modified or banned to a store. Chances are you have already provided the console manufacturer with your personal information so you will be easy to track down by the lawyer calling for restitution for the fraud, or by the police that are going to pick you up, and cart you off to jail.
In synopsis if your stupid it is your fault, but you can still get your money back. Hell you will also probably get your money back with interest. Extortion is such an ugly word, but I also wouldn't lose sleep over a criminal or a pervert getting the screws put to them. Basically all the gripes are unfounded. For these things to happen will be extremely rare, and if they do occur your going to get your pound of flesh. Unless you are the cocksucker in the first place.
Anyway if I was stupid enough to lend my console to someone untrustworthy. First I would hold them up for the cash with interest, to buy a new machine. Now if they didn't give me what I had coming to me I would probably give them a taste of their own medicine. After all everyone has to sleep some time. I would probably go get a can of spray paint, and jack the shit out of their ride. Which would probably be worth all the hassle. A good revenge will fill you with warmth for the rest of your life.