No matter how careful you are, you will inevitably need antivirus and malware protection. Threats from viruses, malware, ransomware, etc are just too common. But I find that no one service provides perfect protection, and buying multiple packages can run into real money. Fortunately there are some good free options.
For many years now I have been a fan of the free version of AVG Antivirus. The free version provides most of the protection you need from virus and other attacks. AVG does have more comprehensive pay versions, but I find the free one meets my needs. Another highly rated free one is Panda Antivirus. Either of these will serve you well for basic protection. They block most viruses and provide other basic protection, with minimal drain on your computer resources.
Getting cleanup help
What happens though when something gets through and infects your computer? If your antivirus did not stop the infection, it's probably not going to be much help cleaning it. You also have to be careful in where you go looking for help. Some tricky malware makers have their own web sites that have free software, or even worse, sell you programs that only make your situation worse. It may remove your existing infection but add others that you don't notice right away. Be sure to trust the sites you are visiting to help with clean up. Be wary of sites that just say download our product. Sites that give more information on the infection and manual removal are more trustworthy, even if they also offer programs to help.
As a computer professional, I am constantly looking for new removal tips for the latest malware. One of my favorite site for advice is bleepingcomputer.com. They have great tips from users and professionals to deal with the latest malware. I find the site trustworthy and helpful.
My go to program for clean ups in Malwarebytes. This program is very helpful to scan for and remove most malware infections. When you install it, just make sure to select the free version. By default, it installs a free 30 day trial of the pay version. If you select the free version, you can keep using it forever for future scans or clean up needs.
No program is perfect. Some malware can avoid Malwarebytes. For a second opinion, I turn to Hitman Pro. This can often find malware missed by Malwarebytes, including some tricky root kits. Hitman Pro is trialware, meaning it is free for 30 days. But you don't have to register it until it finds something and you need it cleaned. You can use it free forever, as long as it does not have to clean anything. To clean something, you need to register for the free 30 days. After that time, you can still use it to check your computer, but will have to pay if you need to clean again. Sometimes I cheat, using Hitman Pro to find things, then remove them manually rather than letting Hitman do it.
Some more aggressive viruses mess with your Internet connection and prevent you from going to certain web sites that give you the tools to kill it. Some may also prevent you from installing programs to kill it. In some cases, I have found Vipre Rescue to be helpful. Vipre Rescue is a free download that you can save to a flash drive, then run on the infected computer. Don't confuse Vipre Rescue with Vipre's main program which is a good, but pay, anti malware program that runs resident on your computer. Vipre Rescue is a separate stand-alone program for removing troublesome malware.
Using a combination of these tools and manual efforts is sometimes needed for removal. Sometimes ripping out this stuff can be a long and painful slog. It's always good to have a backup of your system that you can restore. But I know many don't do this until it is too late. If you do get your system working again, consider it a wake up call and remember to make back ups from time to time.