The information for understanding the threats from virus software is covered in complete detail in other parts of this website. The information on this page is to help you pick the right program for the issue you are experiencing.
Most people call everything that infects a computer a "virus". However, that is not the case,
A virus can spread via email attachments, from files shared from a USB flash drive, DVD, CD or even clicking on an infected online file or email attachment and downloading it to your computer.
Virus are not normally self-propagating, (they don't normally contain the internal code to spread themselves but instead rely on people to spread them to their friends and co-workers.
Many Antivirus programs only notice an attack after you complete a scan of your computer. They do not always prevent you from being infected but allow you to (disinfect) your computer after you complete a scan. That is why it is desirable to run scans frequently or have the program set to scan at least daily. Not all Antivirus programs eliminate all viruses it is up to the user to allow the program to perform regular updates to ensure the program has a chance to remove the newest virus.
The computing landscape has changes and malicious infections can change daily. Today however, most AV programs update daily or more often if needed. Windows 10's Defender performs as good as third party software and it has the advantage of being incorporated within the operating system. To be honest, when Windows 10 was released, I would not have made that claim. However, Defender and the other malicious program protection offered by Window's operating system like "Windows Malicious Software Removal Tool 64 bit" can even remove most virus and malware after you have been infected. things have changed. There are free 3rd party programs that can protect you computer to some degree. The fact that they usually offer two or three better versions should give you a clue that you are not fully protected with the "Free" version. However, Defender is made to be free because it is part of your system. There are no "better versions" that are sold and it is updated as part of regular system updates. If it sounds like I am a fan, I am.
If you were to ask a techie what are the 10 best Antivirus programs you might get a different answer from each, at least in the order they consider best to worst. Included in that list was always a few free versions to help PC owners cut costs where they can. I now eliminate all free Antivirus software in deference to Windows Defender. It is also important to note that Defender also protects against Viruses and Malware. I do not believer there is a Free version close to matching it. However considering the paid versions there are some proven to be better than others and I will start with these:
Norton 360 is considerably more than just an Antivirus program, as the name implies, it protects you in several ways. If you own Norton LIfeLock Ultimate It comes with Norton VPN (virtual private network), Norton Password Manager and Norton 360 as well as several other features like a $1 million dollar protection, 401k, credit reporting and several more features for the primary owner. Another nice part of having Norton LifeLock is all you devices and all the devices of any family member or friends may receive a copy of Norton 360, Norton VPN and Norton's Password Manager for free. If you have a large family and a lot of friends, that is a considerable amount of free software. It carries a big price tag around $300 per year but if you can cover 30 plus devices each with 3 separate types of software, the cost is more than reasonable.
McAfee offers a 2 year 10 device protection plan that is very reasonable. One thing to consider is 10 devices is not that hard to surpass. Just my wife and I with phones, pc's tablets, game boxes, have 8 devices so a large family can quickly to 10 devices.
Webroot is on this list because it is not only an excellent antivirus program but is extremely fast and has a small footprint on your computer. That means it takes very little space and if you are short on disk space a major plus.
Before Defender has reached its current status I used Emsisoft Antivirus. A solid program and it included several newsletters a month explaining tips and techniques to keep safe.
If you don't see your Antivirus listed it does not mean that it is a bad program. I test a lot of programs as part of my job and there are still dozens of antivirus programs I have never tried. I do tend to lean toward software companies with long proven records and each of the programs listed above fit that bill.