You have malware. These "false" warnings that people get like this are notorious. And can be difficult to get rid of without someone who knows what they are doing.
Suggestions -
Go to Add/Remove Programs.
Look for any programs called "Wave Browser" - this has been one of the more common malwares lately. It will also copy itself into random names that have browser as the last word. It might be "Steel Browser" "Lend Browser" - whatever. Remove any program with the word browser - except of course whatever browser you use.
Can't find it? - Do this... the next time you see this message - don't close it - hit ctrl-alt-del and see what processes are running. That window is running in a browser that is not Chrome/Edge etc. It should be towards the top if you click "Memory" tab.
Delete that program.
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