A very good security practice is to take a conservative approach with all communication apps and their features. That means going into the preferences or settings on day one and turning some features off, especially if they're not comprehensible, until you really need them.
This can be tricky because the developer may have taken great pains to provide features it thinks will be helpful, and you'll find that the setting that enables this feature is turned on by default at installation.
For example, every time you upgrade to a new version of iOS, Apple turns Bluetooth on (if it had been off). The reason is that many features of iOS depend on Bluetooth, and Apple doesn't want users to discover that something they thought would work—doesn't.
All this applies especially to Skype. Perhaps because Skype is so seemingly complex, users are happy to to have just it work and don't tend to munge around in the settings. This article will help with that and make sure you have the best privacy settings.
1. Skype Privacy Settings
Our first stop is Skype > Preferences > Privacy. (Here's the official reference page at Skype for OS X privacy settings.) Here's what your settings should probably look like.
A very conservative approach is to not open yourself to strangers. Rather restrict yourself to people you know and have added to your Contacts list. Every so often, I get an unsolicited call from an attractive sounding woman's name who is just dying to chat with me. (You know where that leads, especially if the other end is recording.) For example, if you have ...
- Privacy: Allow calls from anyone = on
- Calls: Answer automatically = on
... then you're just asking for trouble. Anyone you really need to chat with can and should be added to the Contacts list and then specified in all the popups shown in the screen shot above. By the way, the Skype page linked to above explains how to manage blocked callers in the event you blocked someone unintentionally.
At the bottom, leave status on the web unchecked. In fact, it depends on a status button created on a website, which you probably don't have anyway.
2. Skype Calls Settings
As mentioned above, you should elect to receive calls normally instead of automatically. See the screen shot below.
When there's an incoming call (from one of your Contacts!), a dialog box will pop up, and you can explicitly accept or deny. That's a good habit to get into lest your Skype app answers a call you didn't want. (More on the implications of that below.)
3. Skype Advanced Settings
On this page, there are two boxes at the top that you will want checked.
The first is something rather technical, but as you learn more about Skype, you can use Skype > Window > Technical Call Info to diagnose troublesome connections. The second relates to your privacy however. If you've allowed only calls from Contacts, presumably people you trust, then you avoid a situation in which an unsolicited, perhaps malicious caller calls you and then, in the connection process, grabs your WAN IP address. That IP address is easy these days to convert to a city.
By allowing direct connections to contacts only, your WAN IP address is kept hidden, via a relay, with non-contacts. As the description says, that may slow down the connection process, but that's an acceptable trade-off.
The last box on the page allows Microsoft to collect diagnostic information. Read the explanatory note, and decide for yourself.
There are lots of ways for your device to cough up its IP address. Any website you visit can grab it. Any email you send contains it in the header, which is typically obscured for simplicity. Speed test programs will grab it and even echo it back to you. But, in these cases, the connection is initiated by you and the other end is probably not doing anything but logging the data.
So by keeping a low profile in those cases in which someone on the outside wants to intrude or hunt for your location is a reasonable security measure. Remember, no system is completely secure unless it's disconnected from the Internet, but the conservative practices listed above are definitely a good start as you begin to more actively explore Skype's Preferences.