Winrumours.com are reporting a bug in the Windows Phone 7.5 Operating System that allows a SMS, Windows Live Chat message, or Facebook message to reboot the handset and lock users out of the Messaging Hub. The bug, which was initially reported to Winrumors by Twitter user Khaled Salameh, is triggered by a particular message being received on the handset. Thankfully no more information about the content of the message has been made public but it has been passed on to Microsoft who are working to fix the bug.
The Bug seems to affect all Windows phone 7.5 devices on both build 7720 and build 7740 (Mango). The only fix currently is a full wipe and restore.
Winrumors have posted a video demonstrating the effects of the bug which can be seen below.