This indicates a potentially malicious attempt to obtain password information from a system running FTP service.
There exist vulnerabilities in some outdated FTP daemons which allow an attacker to obtain password file on a target machine by system misconfiguration or via a directory traversal technique.
Any unprotected Unix/Linux system that is connected to the Internet is vulnerable to the attack.
Information leak may assist future attacks
Apply appropriate patches or upgrade the system to the latest non-vulnerable version