Most of us know how to protect our computers with firewalls and antivirus software, but we may not know how to sufficiently protect our servers, which store business-critical information. To begin with, turn off all unused ports and eliminate all unneeded software. By deleting unnecessary programs, you reduce the ways in which the system can be attacked. Next, install one of the various free auditing tools available to check for any vulnerabilities or open ports you may have missed. Lastly, install intrusion protection software and plan a strategy for ongoing maintenance.
Unfortunately, keeping your server safe is an ongoing process that involves periodically updating patches and planning for regular security audits.
For more on protecting your computer servers, be sure to read Small Business Network Server Security.