If your computer is running Windows 8 or 10, you can use the built-in Windows Defender to help you get rid of viruses, spyware, or other malware. If your computer is running Windows 7, Windows Vista, or Windows XP, Windows Defender only removes spyware. To get rid of viruses and other malware, including spyware, on Windows 7, Windows Vista, and Windows XP, you need to use Microsoft Security Essentials.
If you’re following common sense and other good security practices, Windows Defender is fine, depending on your risk tolerance. However, if you’re regularly downloading pirated applications or engaging in other high-risk behavior pay for a top end product. One thing with defender it is not going to blitz you with pop up ads and offers or track you to pass on info for profit. I would also consider top end third party security if you are running a business from home on a system that has confidential information or controls accounts containing large amounts of money. Illegal streaming sites, porn sites, etc are the main source of malware, and even with good paid for security you are still at risk if say adobe or youtube are compromised and you use them. Include paypal and amazon to those examples.