MediaPlex

It's adware yes. How it ended up on your PC in the first place I do not know. Could have been you installed some software which bundled it with it, you may have clicked on something you shouldn't... as I said, I really don't know.

We recommend using the freeware versions of both Malware Bytes and SUPERAntispyware, keeping them up to date and scanning with them on a regular basis. Do you also have anti virus and firewall installed?

Are you having any other malware problems?

 

Note that MediaPlex could just be a cookie and cookies are not problems. If you are seriously saying you don't want cookies then you must never open up a browser and must not surf the internet.