Default installation of the Skype installs Skype Add-On (Plug-In) on the browsers. After that, if you browse a page, most of the telephone numbers will be detected.
And look at this if you currently have installed a Skype on your computer: 0044-7987654321
Now the problem is: Skype always sends all of these selected numbers to one of its servers “pnrws.skype.com”. The worst thing is that they are actually sending the page URL in “referrer” section of the header as well. As a result, Skype server can log all of this information with IP address of the user to track a user or to identify a person. And the question is why Skype needs this information?
For proof of concept, I will put a phone number in a Facebook page and monitor the HTTP requests by using Fiddler. The result has been shown in the following images (if you cannot see the images, your ISP has been blocked by GoDaddy):
As you can see, my Facebook URL and the phone number are sent to the Skype server.
However, I think number detection of Skype Add-On does not send more important information such as credit card numbers!
Now, if you are a bit concern about your privacy, just disable the Skype Add-Ons (Plug-Ins) in your browsers.
Please let us know if you know how Skype uses this information and why Skype needs this information.