Someone has either installed Click Potato or it has come bundled with some other application, whilst it is adware (not seriously bad) you don't want it. Using the information in the link given by Pondus you should be able to remove it manually.
However, you may need other tools and malwarebytes anti-malware (MBAM) and avast won't destroy your computer, as you will see from many peoples' signatures lots of us use that combo without problem.