Hi,
first in other countries you may prevent any illegal action against yourself and others with *reasonable* meassures under the "selfdefense" regulations.
But in the case of LaBrea you do not do anything against the other computer. It is more like your neighbour allways parks his car in your garage and you make the entrance smaller so that your car will still fit in but his car will not. I do not think you have to pay for the demages on his car if he again tries to illegally park his car in your garage.
Claiming ignorance ("I didn't know Labrea would crash his PC") will be tricky as in many courts with a civil suit you have to prove your innocence. None of this "beyond a reasonable doubt" stuff/etc as with a criminal case. I wouldn't want to be on the receiving end of a fortune 500 companies lawsuit after all their web servers or whatever got hosed by my machine. Try to remember here, these attacks are NOT intentional. This is a Socual/Policy issue, NOT really a technology issue. Anyways I'm done on this topic for now. BTW analogies suck. This is nothing like car parking/trespassing.
mike
-Kurt