Running a Imac with latest version of Yosemite. The past week; I've been getting annoying pop ups from what appears to be an ad service that highlights key words on anything that I'm working on/reading. This is only when I'm on the internet through a browser (Chrome). I have run a full scan using Avast and Malwarebytes with negative results. I have checked my extension list in Chrome and have found nothing suspicious. Has anyone heard of this annoying bug; and how can I get rid of it?