This stupid shit keeps popping up.
I assume your WiFi network is secured with WEP or WPA instead of WPA2/3 encryption which is why Norton is warning you.
Always has. Always will.
It is glorified bloatware! Crap protection, slows PC down, made to be extremely hard to remove from your PC, Pay for their reviews and #1 rating in review sites, predatory marketing and plan pricing. The list goes on.
Norton has always sucked balls but in this instance Norton isn’t your issue. You’re using older insecure encryption on your wireless network and that’s what the warning is. Pump up to WPA2
Norton always sucked.
But what’s the point of having an antivirus program if you hate that it warns you about threats.
Whenever those pop up, hover over the top-right corner of it with your mouse, where the X is. A dropdown list should appear, click on “never show me again”.
“Norton has always sucked”
I fixed your title for you 
I haven’t touched Norton in about 20 years. No thanks.
Norton for some reason was preinstalled on my version of windows. It was free for a few months so I tolerated it but now I need to figure out how to remove it which I’m sure will be really hard.
Norton always sucked lol.
Is it possible to reduce the effect it has on performance by turning of auto-protect and smrt firewall?
Always sucked.
Windows built-in AV (Defender) and Kaspersky are the 2 only AV I’d ever use.
Add Malwarebyte only for scans/cleanups.
Bingo! You just figured it out! This is pretty cliche on this forum, but the best antivirus is your common sense
Norton has sucked since 2000.
The only antivirus you really need is windows defender 
It had always been that bad.
You’re paying for scareware.
Most 3rd party AV software is bloat on your system. The AV built into Windows is good enough, and the ‘threat’ Norton is warning you of here, what is it actually going to do to resolve the situation? Can it log in to your CPE and change/distribute credentials? It’s essentially useless
I also find the message misleading, is it unsecure with no OR a weak password?
of all the antivirus software out there, I would highly reccomend Kaspersky, it is the best antivirus money can buy (I think.)
either that or windows defender, defender is more than enough for most people unless you pirate stuff and click on advertised google links all the time.
NOW?! I can’t remember when Norton didn’t suck. This has been very well-known among the industry for decades.