Open WiFi probably not a defense...

The dubious defense of an open wireless network as grounds to avoid criminal prosecution just got more dubious: Child porn case shows that an open WiFi network is no defense

The merits of leaving your wireless access point (WAP) open have been discussed and debated at length, especially when it comes to law enforcement. There is a growing belief that file sharers can protect themselves against lawsuits by keeping their wireless access points open. The problem is, it won't necessarily.

The point of clarification here is that: it's still probable cause to go to the place of the open connection.

Read the opinion.