(OT) Google: "Somebody knows your password"

[Volker Wysk]

Hi

I've received a mail titled "Jemand kennt Ihr Passwort" ("somebody knows your 
password") from Google, and a "security warning" mail, with the same contents.  
%-(

Somebody tried to access my google account with my password, from an (to 
google) unknown device. The login was blocked, because of the device being 
unknown to google. I was then guided to change my password, which I did. As 
the location of the unknown device, the mail stated Essen (I live in Berlin).

The mail says (translation below):
"Jemand kennt Ihr Passwort

Hallo Volker,
Jemand hat gerade versucht, sich mit Ihrem Passwort in Ihrem Google-Konto
vwysk1 at gmail.com anzumelden, und dazu eine Anwendung, z. B. ein
E-Mail-Programm, oder ein Mobilgerät verwendet.

Details:
Freitag, 4. August 2017 03:24 (GMT)Google hat den Anmeldeversuch
unterbunden. Sie sollten sich jedoch trotzdem die kürzlich genutzten Geräte
ansehen: ..."

Translation: 
"Somebody knows your password.

Hello Volker,
somebody has just tried to log in to your google account vwysk1 at gmail.com, and 
used an application, for instance an e-mail program, or a mobile device.

Details:
Friday, 4. August 2017 03:24 (GMT)Google has prevented the login attempt. You 
nevertheless should  look at the shortly used devices. ..."

Apart from that, I don't have any information. 

So this means that my Google password was stolen, doesn't it? It was a strong 
password, and I've used it for my google account only.

So how can this be..? And, will it happen again? I have no idea how someone 
could get hold of my password. Sorry for the pointless mail. I'm just a little 
nervous.

Volker