Go to malwarebytes.org and download the free version of their product.
A splendid piece of kit and they have a free version which works well.
Re the original pest, I would bet that what happened was that, during the download/installation of another utility or software, you have to go through the "Accept/Decline" T&C etc. Most people just tick "Accept" without reading the full spiel. (I know I have done it). Read the T&C panel and decline everything other than the software you had wanted to download.