Source of bundled download hinted at, and solution provided.
Whoa! I fired up this Win XP machine today and up pops "Thank you for installing Norton PC checkup. I most certainly did not install this. I've purposely stayed away from Norton for the last 12 years. So I do an alt F4 and it say Norton...will continue scanning...with an OK button. This ain't OK. Any clues about what might be going on here?