How to make a computer invisible in network?

I was amazed that in the left-hand panel of FINDER, under the SHARED tab, there are about 6 other computers that I am seeing. I am concerned that others may be able to access my computer via my wireless connection. How can I make sure I am protected, and my computer is invisible to them?

Set up security as WPA2 Personal with at least a thirteen numeric-alphabetical password.

harryb2448 said:

Set up security as WPA2 Personal with at least a thirteen numeric-alphabetical password.

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That won't make him invisible to those also legitimately in that network, only to those outside the network.

You need to enable stealth mode in the advanced options of the firewall in system prefs.