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A lot of people operate Windows PCs without Norton AV. Uninstalling it will require a reboot. When Norton is gone, Defender will be reactivated by the Norton uninstaller. Windows Firewall will aso be reactivated.
To maintain your protection against drive-by malware downloads, operate your computer account with less than administrator user privileges. If the computer is Windows 7 or 8, that means making your daily use account a "Standard User." This is done via Control Panel > Users and Accounts (or User Accounts).
Before demoting an existing Windows user account, make sure you already have another one with administrator privileges. If you only have one account now, go to Settings > Control Panel > User Accounts and create a new account with Administrator privileges. Assign it a password that you can remember, but is not too easy to guess for outsiders. Log off your existing account. At the Welcome Screen, log into the new admin account. This sets up the desktop and other important settings and folders.
Still in the new admin account, go to Settings > Control Panel > User Accounts (whatever) > Manage Another Account. Find your other previously existing account name and click on its icon to manage it. Inside the user account there is a checkbox to change your account type. Lower it from Administrator to Standard User and apply.
Next, still in the User Accounts utility, find and click on the link to Change User Account Control Settings ("UAC"). Make sure that the slider is all the way at the top (to notify for everything important). Move it up if necessary, apply and exit everything in Control Panel.
Now, log off your new admin account (via the Start Orb/button/icon). Back at the Welcome screen, log into your previous, existing account. You will now be operating as a less privileged user. The UAC prompts that appear when anything tries to change a system setting, install or update a program, or install malware, will require you to type in your admin password. This makes you responsible for your computer security.
Defender will back you up, but only for the most widely known, long existing threats. It will not protect against zero day attacks, or freshly modified Trojan Horse downloads. The UAC prompt will be your last stronghold in these instances.
Note: there are certain types of malware that install into less privileged accounts and remain persistent.
Malwarebytes' Anti-Malware may be able to find and neutralize them.