When wardriving it is inevitable to stumble accross insecure access points and I feel that if I can reasonably guess to whom it belongs (house number in the network name for example), I should do the neighbourly thing and make them aware of their problem and maybe offer adivce on what to do.

Determination to do soemthing is one thing, but deciding where to draw the line is another. Many open access points are open on purpose for example and are not at all a problem. On the other hand, some encryption schemes (WPA-TKIP for example) have dubious weaknesses which are not realisatically explainable to the average person who are not likely fall victim to obscure and complicated attacks anyway.

In the end I decided that WEP enabled access points are the only type worth speaking up about. The Aircrack wiki contains a short tutorial on cracking WEP which is an enlighntening experiance for the uninitiated reader. One finds that breaking into a WEP network takes of the order of 5-10 minutes; which is quite a big and wholly avoidable problem.

Dear Neighbour,

I am a local IT professional. While scanning radiowaves in the area I noticed a problem with your WIFI network. It is currently configured to use WEP (Wired Equivalent Privacy) which is a very old and insecure encryption method. This makes it particularly easy for unscrupolous individuals to gain access to your network, spy on your internet activity and commit computer crimes from your home internet connection.

Contact your internet service providor and ask them for help in reconfiguring your router to use WPA2 encryption. Keep in mind that it is also in their best interest to keep you safe.

Regards
A Neighbour

There may be a small amount of paranoia on my part. I feel it best to remain anonymous, I just want to help, not get sued.