The (closed-source) security software Microsoft ships with modern Windows is quite good.  I don&#x27;t think OSS&#x2F;non-OSS is the real dividing line, but rather motivation of the vendor is.<p>In the case of Microsoft, their motivation is to make Windows work better, in the case of OSS the motivation is often to scratch personal itches, both of these motivations trend towards positive results.<p>In the case of 3rd party security software vendors, their motivation is usually to upsell you from whatever version you are using to a higher level of &quot;security&quot;, so it is in their best interest to go nuts with false positive reports (eg. finding some browser cookies in a scan, posting up such severe looking warnings that you&#x27;d think your system is rooted), bog your system down, etc.