This issue was quickly patched and all Skype users should apply this fix promptly 

http://venturebeat.com/2015/06/02/these-8-characters-crash-skype-and-once-theyre-in-your-chat-history-the-app-cant-start/

Skype users have discovered a rather nasty bug in the app. Sending the characters “http://:” (without the quotes) crashes Skype, and receiving a message with those characters makes it crash any time you try to sign in again.  The bug works as described on Windows, Android, and iOS. It does not, however, seem to have any effect on Skype for Mac nor Skype for modern Windows (the touch-friendly Metro app). We learned of the issue when Skype user “Giperion” posted on it in the community forums. He noted that “clearing chat history not helps, because when skype download chat history from server, it will crash again.”

http://community.skype.com/t5/Windows-desktop-client/Skype-Fix-for-crashes-caused-by-bad-URL/m-p/3997463

We are aware of a problem that was causing Skype clients to crash.  Our engineering teams worked hard to resolve this issue, and have released updates for all impacted Skype platforms. Download the latest version from www.skype.com/download to address this issue.