Sounds like it may only affect those using IE which would mean it caused by an Active X script.
Last night my laptop started acting up, receiving a plethora of error warnings that the computer is being threatened. I saw a half dozen folders and icons on the desktop had gone. I ran my Avast anti-virus scan and still got the same many warnings rolling in. I then wanted to restore the note-book but can now no longer find the program Accessories for the System Restore. It’s just also gone. After the scan and restart I ran Carbonite restore and I no longer get the error warnings, but still missing what mentioned above is gone!!!