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Welcome to Justanswer.com, my name is Dustin.I'm sorry to hear about the issue you are having, I will do my best to help you resolve it.
That message is a scam / virus etc.. if you call them, they will charge you some large amount such as 200$ or 300$ or more to fix an issue that their own virus created.
So , lets discuss removing the virus manually..
Are you using safari on your mac, or ipad, or iphone?