Verizon Internet Security is “powered” by McAfee. If you no longer wish to use the program see the following - - -
https://www.microsoft.com/en-us/windows/comprehensive-security
If you want to use Windows Defender recommend you uninstall the Verizon/McAfee program, reboot the computer, run the McAfee Removal Tool and again reboot the computer. List of anti-malware product removal tools
Defender should be enabled though you may have to start the program in Security Center.
https://www.winhelp.us/configure-windows-defender-security-center.html Good information but ignore the ads.
You might also want to review http://www.howtogeek.com/220232/how-to-use-the-built-in-windows-defender-antivirus-on-windows-10/ Another good article but ignore the ads!
Regards…
http://blog.emsisoft.com/2015/01/27/top-10-ways-pups-sneak-onto-your-computer-and-how-to-avoid-them/