[arturhoo]

As a counter point, I woke up today to this weird email: https://bit.ly/2wMpPL3

Picture is from 2011 and was originally hosted on Picasa (but I'm pretty certain it was never shared publicly) and I don't have a Google Plus account. If I go to the picture itself on Photos, there's no sharing/privacy controls, so I'd assume it is private.

The wording on the email makes it even worse, as if I had intentionally done something overnight to share them on Maps.

[crottypeter]

Perhaps your google account has been compromised?

[arturhoo]

I can't find any evidence that it has been. I use a long and strong password and have 2-step-verification enabled in my account. I haven't received any new account activity emails and the I don't see anything suspicious on myaccount.google.com

As far as I remember, I've never used Panoramio (as a comment above suggests to be the cause). I'd agree that this seems limited to some specific circumstances.