If you're a Skype user, then you probably ought to know about this: Skype 5.8 for Mac, as well as similar versions for Windows, Linux, and Windows Phone, has a bug that unintentionally shares instant messages with other contacts on a user's friend list.
Based on recent Skype customer community posts and our own investigation over the past couple of days, we have identified a bug that we are working hard to fix. This issue occurs only when a user's Skype client crashes during a Skype IM session, which may in some cases result in the last IM entered or sent prior to the crash being delivered to a different IM contact after the Skype client is rebooted or logged in as a new user.
Although we cannot determine precisely how many users may have been affected by this error, we believe the number is small given the very specific circumstances under which the error occurs. At Skype, our customer experience is paramount and we are working hard to release fixes for impacted clients within the next several days.
The Skype clients impacted include: Skype 5.10 for Windows, Skype 5.8 for Mac, Skype 4.0 for Linux, Skype 1.2 for Windows Phone. We urge all Skype customers to download the latest client as soon as they are notified that any update, including this fix, is available.
As of 2 PM GMT on July 17, 2012, hotfixes for Skype for Windows and Skype for Linux are available for download. Although there's no announcement of a hotfix for Skype for Mac so far, you may wish to "Check for Updates" to receive the update as soon as possible. I was able to get an update to version 220.127.116.115, although this page shows that the hotfix version will be 18.104.22.1687.
Update: The hotfix is now available. Once again, using Check for Updates within the Skype for Mac app will locate and install the update, or you can download a completely new installation of Skyle 22.214.171.1247 here.