BestWeb Shoppers pop-up is whats known as adware. Adware promotes lots of websites to trick you into buying software by displaying fake alerts. It is recommended to always read the Terms and Agreements and EULA’s before installing software on your computer, it’s mostly a offer that you accepted and installed adware.
Do never click to fast thru the installation process “Next” or “OK” button of software as you will agree to software you might not want to install. If the installer “Download Client” offers a Advanced or Custom option button, click it to find out if there is any other malicious software offered and installed during the installation process.