Anti-virus and malware protection software. Currently I use Avast free anti-virus and Malwarebytes Premium (I pay $39.99 yearly for the Malwarebytes license)
Having the Malwarebytes Premium gives me 4 active shields against Ransomware, Malware, Exploits and Web protection. So if a website tries to open that has malware, Malwarebytes will have already disconnected even before the site has a chance to open.
Malwarebytes free is also good to have, because then you can at least do a malware scan. I used to use AVG and Spybot, but I always ran into issues. I would scan my computer, and no matter how many times I scanned and cleaned, those two programs kept finding stuff, and no I didn't run those two programs at the same time.
But I do run Avast and Malwarebytes together, as Avast is virus protection, Malwarebytes is malware protection.