Quote from Zed

Fair enough. I'm sure I used to see messages like that on ads before I installed adblocker.

Anyway, first link on google for "ads not by this site": http://malwaretips.com/blogs/remove-ads-not-by-this-site/

Thanks Zed! Now it's gone.

It's actually just a simple malware program that runs and installs that goddamn extension. I read a little more about it just now.
When u get adblocker, it simply doesn't let u see those. But it's still there... Planning it's revenge... xD Jk