Your connection is not private Attackers might be trying to steal your information from bossfrog.com (for example, passwords, messages, or credit cards). Learn more NET::ERR_CERT_DATE_INVALID

Core_issues Said:

"Your connection is not private Attackers might be trying to steal your information from bossfrog.com (for example, passwords, messages, or credit cards). Learn more NET::ERR_CERT_DATE_INVALID"

-------

Clear Temporary Internet Files in Safe Mode:

Having gotten such junk, you should clear your Temporary Internet Files.

If so, Boot into Safe Mode and then Clear your Temporary Internet Files of Safari:

1. Booting into Safe Mode: [hold down shift upon boot until the login screen appears]. See if this is still an issue. Safe Mode lets items run as default, without changes whatsoever. That is possible because caches of your macOS are temporarily disabled while in Safe Mode
2. Clearing your Temporary Internet Files (Cookies & Cache) of Safari: Cookies perform remembrance of certain site-entered data. Whereas Cache keeps a snapshot of the last time you visited a site.  Use this Link: Clearing History and Cache - Apple Communities

Core_issues Said:

"Your connection is not private Attackers might be trying to steal your information from bossfrog.com (for example, passwords, messages, or credit cards). Learn more NET::ERR_CERT_DATE_INVALID"

-------

Report this to Apple:

That is a scam. So, take a screenshot of this, and send it to Apple. Add it as an attachment and explain to them what this eMail is all about: A phishing scam report. Go Here: Take a Screenshot on your Mac - Apple Support. Send the eMail to: reportphishing@apple.com

I've been getting exactly the same message for the past 2 days on about 25% of the sites I visit now. It's not a Safari issue. I've tried 4 different browsers and cleared all caches & cookies. I can't access my Protonmail and even Brave browser support site is unsafe (while using Brave browser!!). My date is fine. I've changed no settings and have no updates waiting. I am using an older iMac so I'm wondering if that's the issue. It's been reliable all these years. What should I try next?

One problem seems to be that a third-party issuer of certificates, "Let's Encrypt," let some expire at the end of September:

https://scotthelme.co.uk/lets-encrypt-old-root-expiration/

If site had been using that service, and are not secure, they will not open on older versions of Safari like included with os 10.11 and may error in newer versions.

FireFox may handle certs differently than Safari so see if that works.

This is what I get for many sites. I'll send to Apple. Thanks.