A company stealing other company's Wi-Fi - is it legal?

A friend recently posed an interesting question:

"What if someone in an office building with multiple companies in it used another company's wi-fi signal without that company's permission? What part of the law would be broken, if any? Also, could that company sue the person using the wi-fi signal without permission?"

So I went to the Net.

I remember when this story happened:
http://money.cnn.com/2005/07/07/technology/personaltech/wireless_arrest/index.htm

And this just makes it sound murky.
http://money.cnn.com/2005/08/08/technology/personaltech/internet_piracy/index.htm

Does anyone know? CONTACT: Leave me a Houston or Texas media news tip | COMMENT: Click to leave your thoughts on this post here