Hello whonew -
PUP.Optional.Amonetize, and several other items described as PUPs are "technically" not a virus, but it does exhibit plenty of malicious traits, such as rootkit capabilities to hook deep into the operating system, browser hijacking, and in general just interfering with the user experience.
These can later cause major problems.
They are generally refered to it as a PUP, or Potentially Unwanted Program.
Malwarebytes Anti-Malware is now more sensitive to these "potential threats" and stops them prior to allowing them to install on your system.
The PUP.Optional.Amonetize infection is used to boost advertising revenue, as in the use of blackhat SEO, to inflate a site’s page ranking in search results.
PUP.Optional.Amonetize got on your computer after you have installed a freeware software (video recording/streaming, download-managers or PDF creators) that had bundled into their installation this browser hijacker. This Potentially Unwanted Propgram is also bundled within the custom installer (Wrapper) on many download sites (examples: CNET, Brothersoft or Softonic), so if you have downloaded a software from these websites, chances are that PUP.Optional.Amonetize was installed during the software setup process.
Always try to use the Makers site to install programs from, and not random download sites -
Basically you have done the right thing, and always remove PUPs when found -
Thank You -