You do get a free copy of Windows Defender with Windows 10 and it works fine. There are better alternatives out there and for the most part. You can get by with a free alternative.
I've tried several different free Windows anti-virus and malware protection suites and I found a few that I like. On some computers I use the free software from Avast A.V. A.S.T.
I read an article recently that said that an Anti-virus AVIRA is a useful and good product.
We have an article linked on our website which describes the current, Five, Best, Free, Windows security systems. And you probably should find one of them from that list to install on your Windows 10 computer. This article link was pulled because there was some questionable Anti-Virus products.
Certainly you don't want to go out there in the wild world of the Internet without some sort of professional Anti-virus product installed on your computer.