Ipswitch WS_FTP Server 4.0.2 has a backdoor XXSESS_MGRYY username with a default password, which allows remote attackers to gain access.
https://exchange.xforce.ibmcloud.com/vulnerabilities/15558
https://euvd.enisa.europa.eu/vulnerability/EUVD-2004-1877
http://www.securityfocus.com/bid/9953