I am periodically getting popups in both Firefox and Chrome. In Firefox something blocks the popup itself (probably Adblocker) so all I get is a little 'x' in order to get rid of it, which saves me from the worst of it but is becoming very annoying. Additionally, sometimes when I click on a link I get redirected to some website or another trying to sell some terrible product (typical advertising website). Neither of these things happens every time, but occurs periodically. I have done multiple scans with Microsoft Security Essentials and Malwarebytes to no avail. They turn up clean, but there is definitely something there that I cannot seem to get rid of.

Has anyone come across this issue before, or know what it's called? I can't even effectively google search becuase it's so vague.