rick,

have a look here:

Closed vs. Stealth Ports -- My Views

Major computer security companies, such as Norton, claim that they can "hide" your PC while on the Internet by "stealthing" your ports. People with greater knowledge know that "stealthing" doesn't really help anything, yet the general public keeps on believing that ports have to be stealthed or you're not secure. In this article, I tend to show you that stealth ports aren't any better then closed ports, and sometimes "stealthing" can be bad.

To be able to explain my views, first you must know how a firewall gets a port scanner, such as GRC.com's Nanoprobe, to return "stealth" instead of open or closed. It's very simple. When a TCP connection is attempted to a "stealth" port on your computer, your firewall simply does nothing; it drops the packet. (As a side note, dropping packets blindly actually breaks RFC compliance.) Whereas with closed ports, the OS or firewall replies with a packet that has the RST flag set.


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