If you never installed the Norton product, then it's obviously malware, probably not from norton. If it's a stand alone window ad, always try and use alt+f4 to close it. Clicking on any x or close in the ad's window just tells it you are live. That fact that it spans all browsers gives me the idea it's installed in some folder on your hard-drive.
Clean out all your temp internet folders, then find and clean out any windows TEMP folders as well. Windows still keeps a temp folder or two around for various reasons, but if you have not installed or changed anything in over 10 reboots, it's safe to delete these temp folders too.
It's actually a good thing as lots of malware installs themselves there because they know most people don't know or care about these folders.
If this action doesn't help, you'll need to run something Malwarebytes or other legit malware scanner prog.
Good luck.
