With the default privacy settings, anybody else using Microsoft's Skype service can search you out and call you, but you can change your visibility so that only people you have added to your Skype contacts list can contact you. (These same default settings keep your Skype profile picture hidden from anyone who is not already on your contacts list, though.)
To change your Skype settings, log into your account. Under the Skype menu in the Mac's upper-left corner, choose Preferences and then click the Privacy tab in the box that pops up on screen. Next to the "Allow calls from:" line, choose Contacts instead of Anyone. If you have signed up and paid for a Skype Number, you can change the settings for that as well so that only people on the Contacts list can call you there.
People who want to call you must now send a request to be added to your Contacts list before they can call you. If you know people using Skype that you would like to add to your Contacts list, you can send a request yourself.
Recent versions of Skype also allow you to link your Facebook and Skype accounts together so that your friends are all grouped in a Facebook section of the Contacts list. (Later, if you decide connecting your Facebook and Skype accounts is too much social networking, you can always unlink them.) To make sure you are using the latest version of Skype for Mac OS X, open the program and under the Skype menu in the upper-left corner, choose "Check for Updates."
—nytimes.com
