[rabscuttle385]

Is it legally or morally ok, therefore, to send viruses to the computers stealing/sharing the bandwidth?

I don't think so. That would fall under "destruction of property." You can, however, forcibly kick them off your network by properly securing the network so that it denies unauthorized access attempts. Plus, if they get away with a virus-infested computer, they can infect other networks and systems.

Now, a friend of a friend set up a trap on his wireless network so that any unauthorized nodes would be commandeered, their hard drives wiped, and Linux installed.

[Myrddin]

Now, a friend of a friend set up a trap on his wireless network so that any unauthorized nodes would be commandeered, their hard drives wiped, and Linux installed.

That would be vandalism. Your friend's rights stopped when he inflicted damage on the other system's hard disk. Had he stopped at logging the MAC address and barring further communication, he would not have had a problem. What a lovely tort the victim would have if his business records were destroyed. There might even be criminal penalties if the act occurred in a state with the appropriate laws on the books.

[Blue Highway]

Now, a friend of a friend set up a trap on his wireless network so that any unauthorized nodes would be commandeered, their hard drives wiped, and Linux installed.

You hear stories like this from time to time, but I have to say it sounds more like fiction. How does one issue commands from a router to format someone elses hard drive and install Linux?