The campaign originates from within Iran, stated Eric Grosse, Google's VP of Security Engineering, and has been going on for the last three weeks.
The sent email looks claims to be coming from Google, and urges users to add an alternate email address to their account:
"Our Chrome browser previously helped detect what appears to be the same group using SSL certificates to conduct attacks that targeted users within Iran," noted Grosse.
"In this case, the phishing technique we detected is more routine: users receive an email containing a link to a web page that purports to provide a way to perform account maintenance. If the user clicks the link, they see a fake Google sign-in page that will steal their username and password."
Potential targets will also be warned via an alert that will pop up above their Gmail inboxes no matter what browser they use, and are urged to consider enabling 2-step verification for their accounts and to be careful that the page into which they type their Google credentials is the following: https://accounts.google.com/.