Windows Defender is software that helps protect your computer against pop-ups, slow performance, and security threats caused by spyware and other unwanted software
The number one anti-malware tool is the one that gets the least attention – the anti-stupid program that should reside inside that hard drive on your shoulders.
Sorry, but it really doesn’t matter what you might think it is, as anti-spyware applications are different to anti-virus applications, whilst the edges are blurred, most are designed to work with AVs.
This you can see by a number of forum members signatures indication that they also have anti-spy/malware applications along with avast.