Anti Virus Software

I ask because I've been having a lot of issues with my Mac including it freezing, not responding to anything for long periods and me having to force close apps in order to get anything to work. ...

Please determine if the same problems occur in "Safe Mode": tUse safe mode on your Mac - Apple Support.

A couple of points:

• No you do not need Anti-Virus and doing so will most likely cause more harm than good.
• Norton Ads will pop up for anyone and happens more when visiting less legitimate sites. In this case it is the site that is making the ad look like a system message to trick you.
• Another common Norton message comes up as a Notification when you have allowed a web site to send Notifications to you. These can be checked at Safari > Settings > Websites > Notifications. Start by denying all the all the websites that are set to Allow. If you do want a Notification from a specific website you can turn it back on after verifying that the Notifications have stopped and then be able to tell which one is giving you the fake notification. The same can be done in the Pop-Up Windows setting.

As for the slow response and freezing apps, I would recommend running the free version of EtreCheck and post the results here using the Additional Text option. EtreCheck will not change any files, but will provide a view of your System showing apps that are running on startup that could be slowing things down for you. EtreCheck is a safe app developed by a member of these forums and does not include any personal information in the report that you post. It will give the details needed for other users here to offer suggestions to improve the performance of your Mac.

Using EtreCheck

It's a scam. A scare tactic to get you to buy an app you don't need

Issue with your Mac might be because of installing an AV product, but not installing one is not going to cause problems.

Describe your problems in detail ands help may be forthv=coming.

Read Stop unwanted Notifications - Apple Community.

Pull quote:

"Website notifications are not viruses and they are not malware."