It doesn't take long to figure out the security problem with these port technologies: If a port lets data flow out, it also lets data flow in. A port is essentially an opening into your computer, and it can be hacked. . . .
It doesn't take long to figure out the security problem with these port technologies: If a port lets data flow out, it also lets data flow in. A port is essentially an opening into your computer, and it can be hacked. Someone can infect your machine with a Trojan horse in this way, and that's only one of a host of distressing possibilities. If you open your computer to the outside world, you're vulnerable to attack -- period.

Port-scanning software tests your network to determine which TCP ports are vulnerable to attack. These programs analyze typical TCP ports by default, including HTTP (port 80), Finger (79), FTP (21), NNTP (119), POP3 (110), SMTP (25), and Whois (43); you can specify additional ports if you use them (8080 for a Web server, for example). Depending on the program, you can scan individual IP addresses or ranges. Keep in mind that scans take a widely varying amount of time to complete, from seconds to hours.

The purpose of port scanning is to determine vulnerability to port attacks. Still, that knowledge by itself will only increase your networking fears; the whole point to determining vulnerability is to do something about it. That's where firewall software comes in. Once you've scanned your ports, you can customize your firewall software to monitor and even prevent traffic to and from the vulnerable ports, thereby reducing the risk considerably.

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