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Introduction to Port Scanning
A sure way to see what you have running is to port scan your own system (IE localhost). Port scanning is also a good technique to test firewall rule sets.
Port scanning is an important initial step towards knowing yourself. If you don't know what services you have running, it will be impossible to secure them from malicious crackers. It is also important to familiarize yourself with port scanning programs so you will know your "enemy", system crackers, who will often employ a port scan to determine if you have an exploitable service running.
Advanced port scan tools will even do TCP/IP stack fingerprinting, allowing an attacker to determine what operating system you are running, often down to the kernel version!
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