"It has been discovered that during Windows shutdown, Outpost does not block traffic allowing unsolicited incoming traffic to access systems for a short period of time. This depends on system configuration but testing has shown this to be in the region of 3-10 seconds (though a 20-second window was encountered in a test with Outpost 2.7). While this issue was discovered with Outpost 3.0, all earlier versions of Outpost should be assumed to be affected also."
Source: Outpost Firewall ForumsÂ»
Note; This may also occur during startup: