You do not need to purchase any additional Virus Protection on Windows 8/8.1/10 PCs, they all come with the following sufficient layers of security integrated. The order in which I list them is the order they will operate and give warnings to you as you go through your daily PC usage:
1.) Internet Explorer/Edge SmartScreen Filter, which scans websites you visit and files you download via Internet Explorer/Edge, and uses a dynamic database of known malicious websites/files on Microsoft's servers (a.k.a. the Microsoft CLOUD) to determine if the website and/or file you're downloading is safe. If anything is suspected it'll show a warning message in place of the website or once the file is downloaded.
2.) Windows Defender, which is an Anti-Virus/Anti-Spyware/Anti-Malware itself. However, it's based on a local-only malware database, which isn't always up to date, that's what the next layer of security fixes.
3.) Windows SmartScreen, which scans files (from any source) and web content (be it via Windows Store apps or any other Non-Internet Explorer/Edge web browser you use), and uses a dynamic database of known malicious web content/files on Microsoft's servers to determine if the web content and/or downloaded file is safe to open. Again, if anything is suspected, it'll show a warning message in place of the web content or before the file is opened.
4.) Windows User Account Control (UAC), which is the last line of defence for every application you run on your PC (it's been there since Windows Vista). If ANY executable file (which is what every type of malware comes as, but not all executable files are malware) wants to run on your system, it'll alert you, requesting your permission (depending on what you configure it to). You can even configure it to request your password whenever an executable wants to run.
If you have all of the above enabled on your Windows 8/8.1/10 PC, you don't need to buy any other Virus protection. However, like any other security software, criminals are always on the look out for holes in them. The best and safest way to avoid any malware concerns is to simply think before you click. I've been practicing that for over 7 years now, and no malware has been able to beat that and make it to my system...coming from a guy who does a lot of torrenting...in fact, I personally think the Windows UAC security layer is too much baby sitting, and I confidently have it set to never alert me, 'cause I'm self-aware of what runs on my system, so, no need to tell me a second time, but that's just me.