Hello Volleygirl56,
Does this website appear whenever you are browsing the web? Or does it appear only when you are on certain sites?
There are many web scams that will display these notices. You can just ignore those and try to stop going to those sitrs.
Unfortunately, this could also be caused by adware installed on your machine. If that is the case then you won’t be able to escape it until you remove the adware.
I wrote a little diagnostic program to help show what adware is installed. Download EtreCheck from https://www.etrecheck.com, run it, and paste the results here. EtreCheck is perfectly safe to run, does not ask for your password to install, and is signed with my Apple Developer ID. When you are done, EtreCheck can be thrown in the trash.
If adware is installed, EtreCheck will help you remove it, although you may have to supply a password. If you aren’t comfortable with that, just post the EtreCheck report here and other helpers can tell you exactly what files need to be deleted and how to do so.
Disclaimer: Although EtreCheck is free to download and use at first, it will eventually ask you to buy a license. There are also other links on my site that could give me some form of compensation, financial or otherwise.