I'm sorry that I'm not very familiar with Webroot and have never used it, so can't say for certain whether it's causing issues for your or not. macOS Security Update patches were discontinued over two years ago. As you probably know, Apple anti-malware support of El Capitan is currently limited to background updates for Gatekeeper, XProtect and MRT (Malware Removal Tool) as long as you have 'Install system data files and security updates' enabled in System Preferences->App Store.
I don't know enough about your computer skills and practices to give you a completely accurate answer, but in general you should be reasonably well off without and additional anti-malware (viruses are just one form of malware) software.
