Any remote access that takes a plain text password increases the vulnerability of your system. This includes the use of telnet and FTP.
If your flavor of Unix is running the inet daemon, you can disable telnet, ftp, rlogin, and so on by accessing the /etc/rc.conf file and setting the inetd_enable value to no:
inetd_enable=no
You can disable individual services by accessing the inetd.conf file and setting the associated line to no, or commenting the line out, as shown in Darwin and BSD environments such as OpenBSD or FreeBSD:
#telnet stream tcp nowait root /usr/libexe/tcpd telnetd
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