What is Mighty Magoo?

Every now and then, wherever I'm browsing (any site, anywhere; it's totally random) I get a word or phrase that looks like a link but it's not. It's blue, but underlined twice instead of once, and if I hover over it I get a "Mighty Magoo Games" box. I researched and I see that Mighty Magoo is a legit game site but I don't understand a) why the ad shows up at all and b) how it's taking random words and phrases that are different each time (even within the same site the same day) and "making" those words a link to their site. Trend Micro keeps notifying me they've removed it but it shows up several times a day. How do I get rid of it for good?