Odd message suddenly showed up on desktop

I have an ASUS laptop running Win7 home premium 64-bit OS .. had this for 4-5 years now and it's been a great computer. I will admit to being somewhat of a tinkerer and I download & install just about every piece of free software that I can find, and then either delete it, or forget about it :) Just yesterday, a strange message showed up on the bottom corner of my desktop (see screenshot) that says "Test Mode Windows 7 Build 7600" .. I've searched my desktop directory and also turned off the desktop and this message is always there .. I changed my windows background and still, the same message. I ran several virus checkers (spybot, Avira) and cleaned up my trash & other stuff (ran CCleaner and Glary Utils), then I rebooted ... still have that message ..

Anyone have any idea what might be going on?

Thanks!
george c

Scan with Malwarebytes Anti-Malware free too just in case.

Do you have a System Restore point from before the message showed up that you can restore? System Restore

This should solve your problem:
https://support.microsoft.com/en-us/kb/2509241

The computer is in a special mode that allows unsigned device drivers to be installed. Not a good idea for most people but useful to developers. Most likely it was enabled by some software you were trying.

thanks to all for the quick responses! All were helpful. I followed the link given in several replies and clicked on the 'fix it' button etc, and was prepared to do the 'restore' that other replies suggested as a backup remedy (which, I must admit, I feel pretty foolish for not thinking of). This is a great forum :)

georgec32