For Windows 10 users, I can confirm removing KB3093266 which just came down will fix Windows Live Messenger 2012 again. The cumulative update includes a Skype update which seems to break WLM.
Once you are back online you should take advantage of the Microsoft too to Hide Updates for Windows 10.
This is available from here https://support.microsoft.com/en-us/kb/3073930
Happy days and long live messenger.