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I'm also somewhat new to Mac, but learning quickly. I found this same problem on my Mac this afternoon - have never seen it previously. No new software downloads, the most recent installation was the newest security update from Apple. The one thing I recently changed was in System Preferences in the Security Section. I had the firewall running previously, but recently added Stealth Mode to my settings (just as a precaution based on articles I read). After finding the Google problem this morning, I did a search for the issue and found the forums here - read the posts on this subject as far back as I could find. Nothing anyone else spoke of seemed to apply to me - no new installs, never had the problem before, had tried resetting Safari, restarting computer, and so on. The only thing I could think of was the newest update from Apple (which installed last night before I went to bed) - and I remembered changing the security setting about 2 days ago. I went to Firewall Settings, removed the check from "Stealth Mode". After removing the checkmark, I went back to Safari, expecting that I would need to restart Safari and maybe even restart my Mac, but to my surprise the yellow triangle was gone.
I don't know enough about Mac to say for sure this is the solution for everyone else - just adding my experience & hoping maybe it helps someone out there.