I don't know if it is a know technique, but in the last month I received a lot of legit email from Google that somebody is trying to set my email address as their gmail backup address.
At the beginning I ignored these emails, I clicked on unlink this account in the message body, then I decided to change strategy. I reset the password of some of these automatic gmail account and I tried to became the new owner.
Most of these emails come from Mexico or USA, how do I know it? Google tracks the activities since the beginning.
I still don't know if these emails are automatic or made by real humans.. but I think that are from bots because the pattern are always the same <3randomchars>@gmail.com .
Is it happening to you too? Maybe some bots have cracked Google captcha again? I'd like to report this to the Google support but I don't think they care much.