Enhanced Safe Browsing was released in 2007 as an upgrade to Google's standard Safe Browsing feature that warns users when they visit known phishing and malware sites.
That's gotta be a typo. Gmail itself came out in 2004, and I doubt that "Safe Browsing" and then "Enhanced Safe Browsing" both came out in the first three years.
I'm guessing it's supposed to be 2017?
Regardless of when it came out, the nagging prompts sure are annoying.