Initially, the blacklist is empty. You can type in a callsign-SSID combination and click the Add Callsign button to mark that station for blocking. Similarly, if you determine that the station should no longer be blacklisted, you can select it on the list and click Delete Callsign to remove it from the blacklist. You can also select to what level the station will be blacklisted by choosing whether to stop it from being I-gated (either to or from the APRS-IS) or digipeated, and whether or not your station will respond to queries and/or inbound AX.25 connection requests from that callsign-SSID. Note that you can't stop receiving the offending station (because you can't make them stop transmitting), but you can make your station stop being an accomplice to their behavior. If you also wish to stop seeing the offending station on the YAAC displays, use the Filter->Edit Filter menu choice and disable the source callsign-SSID on the Sender tab.