Security is complex and takes time to learn. The best thing to do is to get a scan of your box from a tool like ISS or NESSUS. Then evaluate the report and take actions as necessary. Important things to consider:
1 Comment unused services out of inetd.conf
2 use inetd.sec for used services
3 get away from telnet/ftp and use ssh
4 lock down sendmail (edit sendmail.cf and use something about 8.8.6)
5 use securetty to control root logins
6 use ftpusers if ftp is required
7 log, log, log. Use the -l options in the /etc/rc.config.d/netdaemons file
the list goes on...
A good book on this is the O'Reily book on security. They have ton's of suggestions.
Hope this gets you going
"In theory, there is no difference between theory and practice. But, in practice, there is. " Jan L.A. van de Snepscheut
