ReCaptcha does not let me log in

When I try to log in to the wordpress dashboard I see a reCaptcha page that says:
This page is an extra security measure for websites which use WordPress or Joomla!. Before you can log in, you have confirm that you are a human being. You can do this by confirming the reCAPTCHA above.”
And the captcha says:
ERROR for site owner: Invalid site key
This happened to 5 sites out of 10 i am managing.
Disabling/removing plugins did not help. Also I do not remeber setting up reCaptcha anywhere except Contact Form 7. Captcha on contact forms works fine.

So I think it is built-in feature, because this captcha thing appeared sometime ago on all websites at once.

I am really puzzled. Does anyone has any ideas what can i do with this?