With Skype 3.8 for Windows beta we have made our own UPnP implementation which is no longer dependent on Microsoft UPnP framework.

UPnP is an industry-wide protocol designed for automatic device configuration. Its main purpose is to provide seamless "just works" experience when a new device is connected to network.

Most major consumer router vendors are using UPnP in their devices. Skype uses UPnP to configure the firewall for best possible call quality.

Since Skype version 3.0 Skype has relied on Microsoft UPnP Framework to configure devices. However there are a few concerns if UPnP Framework is used in conjuction with Internet Connection Sharing as described in Microsoft knowledge base article 886257. Due these issues Skype provided opt-in check box under advanced connection options.

Skype for Windows version 3.8 has new UPnP implementation which does not depend on Microsoft UPnP Framework anymore and hence issues outlined in Microsoft KB article do not apply anymore. Along with that change "Allow Skype to modify my firewall settings" checkbox has been removed. Since Skype for Windows version 3.8 the UPnP is enabled by default.

New UPnP implementation is already available on Skype 2.0.0.68 for Linux and will come to Mac users soon.

People who are concerned with overall UPnP security should disable UPnP on their firewall device. For assistance see your firewall manual.