Wireless Unknown Access Points
Observer has sensed an Access Point not on the list of known Access Points defined by MAC address in the Expert Thresholds settings.
Possible reasons for the event:
Someone is trying to set up an unauthorized Access Point on your network.
Ad-hoc networks generate arbitrary, spoofed AP MAC addresses as part of normal operation, so an Ad-hoc network may be the cause.
Observer is seeing traffic from a nearby AP or Ad-hoc network unrelated to your network.