Even if you download the free version of Malwarebytes if you are not careful right at the end of the install it asks you if you want to run a trial of the premium (paid for) version.
This is ticked ON as default so if you don't untick it you will get a trial of the premium version and not the free version.
Actually probably the best protection is to make sure you install all the Windows updates as they come out and keep all your other programs up to date.
Many of the Windows updates are security fixes and if you don't install them you are leaving yourself open to hackers.
When Microsoft find a security hole they publicize what the "hole" is and so the hackers write code to exploit it.
If you don't install the latest Windows update you are leaving that security hole wide open.
You can set Windows updates to install automatically.