Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address Foreign Address State
tcp 0 0 0.0.0.0:587 0.0.0.0:* LISTEN
tcp 0 0 0.0.0.0:6000 0.0.0.0:* LISTEN
tcp 0 0 0.0.0.0:25 0.0.0.0:* LISTEN
udp 0 0 0.0.0.0:68 0.0.0.0:*
Ports 25 and 587 are used from sendmail (mail server)
Port 6000 is the X-server
As for port 68 according to /etc/services is used by bootpc.
If you don't use sendmail and bootpc you should disable them, or use a firewall to block respective ports.
sendmail is started from /etc/rc.d/rc.M but I don't know about bootpc.
to see if it tells you how bootpc is started (from inetd or standalone)