You may have gained some adware when downloading or installing something recently. One has to keep eyes open for unwanted "add-ons" at all times. I wouldn't imagine it's not dangerous but just in case run AdwCleaner and MalwareBytes Free from the last link below.
Also check your installed toolbars as that may be listed there. See the instructions on that link on how to keep Malwarebytes free of charge.
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