chan_sip.c: Hanging up zombie call. Be scared

We are using asterisk version 1.8.7.2
Recently in asterisk log file, I notice this line:

DEBUG[7145] chan_sip.c: Hanging up zombie call. Be scared.

What exactly does this mean? Do you have any ideas why it happens and please suggest possible solution.

Thanks in advance.

Debug messages should be ignored unless they are associated with real fault symptoms.

A zombie channel is the one left over after a “masquerade”. If you don’t understand that, it is not something that can be explained quickly.