The current version of Califoria Assembly Bill 2415, as last amended on August 21, 2006, may make it much more difficult to prosecute someone who piggybacks off someone else’s wi-fi service that is not password protected.
It states that:
There is disagreement as to whether it is legal for someone to use another person’s WiFi connection to browse the Internet if the owner of the WiFi connection has not put a password on it. While Section 502 of the Penal Code prohibits the unauthorized access to computers, computer systems, and computer data, authorized use is determined by the specific circumstances of the access. There are also federal laws, including the Computer Fraud and Abuse Act (18 U.S.C. Sec. 1030 et seq.), that prohibit the intentional access to a computer without authorization.