Over at the Volokh Conspiracy, my friend Orin Kerr has a fascinating post on the case of US v. Stanley. It isn't strictly cybersecurity but the case itself is still worth reading. For those who want a quick summary:
The police traced a child pornography download to a particular IP address. Executing a search warrant at that address they found nothing at all. Turns out someone outside the apartment was freeloading on the owners unsecured wireless hotspot. With the consent of the apartment owner, using a technology known as "Moocherhunter" (naturally), the police traced the moocher to a nearby apartment. A search warrant was executed and child pornography was found on Mr. Stanley's computer. He argued that the use of Moocherhunter was itself a search under the 4th Amendment but, relying on third party doctrine developed by the Supreme Court in Smith v. Maryland and US v. Miller, the district court concluded that Stanley had no expectation of privacy in the wireless signal emanating from his computer.
I agree with Orin that this is probably the right result under current doctrine. And that it is a truly fascinating set of facts.