Critical to keeping your computer in top-flight condition and making sure that your personal information remains PERSONAL, anti-virus and anti-malware programs are essential in this day and age.
For anti-virus, I am very partial to AVG and have used it on all of my personal computers for several years. They offer a free version that is a very good product. They also have a paid version that includes some extra features that are not available in the free version.
I wish that virus software was enough, but I have found that often it is NOT. Spyware and Malware are different from viruses, and require another software version. MalwareBytes is a great program that I use in spyware/malware cleanups all the time. They have a free version, but the enhancements available in the paid-for version are well worth the small, one-time fee for licensing the full version. The full version unlocks realtime protection, scheduled scanning, and scheduled updating, all critical for the software to keep you protected without you having to think about it.
In my opinion, spending a little bit of money on security and peace of mind is well worth it...and if you do not agree, both of these products have a free version that will offer you some protection anyway!