The security bug stems from a format string error in the Skype URI handler. The flaw creates a potential means for hackers to create a maliciously constructed Skype URL which, if followed, might allow them to inject hostile code onto vulnerable systems.
Security company Secunia has the bug duly noted, and anyone using Skype should download the update. This comes just a few days after Apple releases a host of updates for OS X. It's been a busy week for Mac users.