I took the free upgrade to Windows 10 about a week ago. An unknown second user has started appearing on the password log-in screen. It has the name 'smmosbvjntf'. It is easily removed from the user account box but usually reappears on the log-in screen within 24 hours.

I also get a pop up from Tweakbit which wants me to use it to clean up my computer. I'm ignoring that.

I subscribe to Eset and have scanned my laptop several timesusing the Eset scan and have come out with a completely clean bill of health.

Any suggestions of how to rid myself completely of this unknown second account user?