Wardriving, detecting open networks, is legal. You drive around with a laptop equipped with your wireless networking card and sniffing software to find wireless protected/Unprotected access points .
There is however a small problem . . . once you open your browser, use the signal to get into someone else’s wireless network, Simply opening your browser as you are “passing through” to check your email is somewhere in-between shades of gray.
( in USA maybe , in Sweden the responsibility rests on
the Person who doesn't/hasen't protected his wireless network,
still, even then it's not a very nice behavior )
'Spy threshold crossed', means that the signal strength for one of the addresses in the/your spy list went under the low threshold or went above the high threshold as set by your driver/software.
(; As i understand it...The lower you're 'spy threshold' the smaller 'footprints' you leave behind when you're, well hmmm
)
Such events will be generated on some wireless interfaces by the wireless driver, and their support depend on the specific hard-ware/driver combination. Check your driver documentation for details on what's possible.
