I am frequently asked what is the best way to protect computers from malware and viruses. If you've come to this page looking for an antivirus program that will guarantee you will never get another virus, keep looking. I doubt you'll find such a page because I haven't encountered an antivirus program which blocks 100% of all viruses and threats. While you certainly can pay for protection, you can usually choose from any of several free options to protect your computer from viruses and other threats. If you take a good, free security product and combine it with responsible web browsing, you can prevent most problems that get users into trouble. I generally encourage people to avoid things like Spybot Search and Destroy and Malwarebytes because Windows 10 isn't as resilient as Windows 7 and these programs frequently cause Windows 10 to break when you're trying to fix it.
For home computers, if you are not running a business from it or using your computer for work, you can install AVG Free Antivirus software which is a great and easy-to-use free software package available from AVG Technologies. While AVG is a good product, one thing that I don't like about it is that it can be somewhat pushy about suggesting computer tune-ups and trying to sell your their full version. Lately I have been recommending that people instead download and install the Avira free antivirus software which does a great job of notifying you if it detects a problem with a file you are attempting to access but it stays out of your way and doesn't bother you with needless messages for the most part. That, in addition to not impacting the computer's performance or slowing it down, are two of the most important things I look for when selecting my protection.
A free anti-spyware program called Microsoft Security Essentials is available from Microsoft to all users of Genuine Windows 7 (pirates need not apply). It provides regular updates as new threats are identified, and identifies and removes all kinds of junk software and threats. I like it quite a bit.