I am aware of this Extension(If you are a google chrome user), infecting many people. This thing found my way through either downloading Minecraft Mods, or that eyeliner from TSR.
Basically, what Price Chop does is inject pop-up ads everywhere. You may also get unwanted pop-ups.

There is a helpful guide on how to uninstall PriceChop and get that nasty thing off of your computer. http://malwaretips.com/blogs/remove-price-chop-virus/