sending the magic shell string but before sending a shell command.
Michael Meyer reported that the script would sometimes fail to report a
backdoor; I tracked this down to the sends happening in too-close
succession. The ProFTPD process could receive both sends
("HELP ACIDBITCHEZ\r\nid;\r\n"), read the first line, and execute the
shell, but then the shell would get no input because the "id;\r\n" had
already been read.
This causes a delay up to the timeout when there is a backdoor, but it
still returns right away when there is no backdoor.