TLDR: Government-backed phishing has been in the news lately. If you receive a warning in Gmail, be sure to take prompt action. Get two-factor authentication on your account. And consider enrolling in the Advanced Protection Program.
One of the main threats to all email users (whatever service you use) is phishing, attempts to trick you into providing a password that an attacker can use to sign into your account. Our improving technology has enabled us to significantly decrease the volume of phishing emails that get through to our users. Automated protections, account security (like security keys), and specialized warnings give Gmail users industry-leading security.
Beyond phishing for the purposes of fraud, a small minority of users in all corners of the world are still targeted by sophisticated government-backed attackers. These attempts come from dozens of countries. Since 2012, we've shown prominent warnings within Gmail notifying users that they may be targets of these types of phishing attempts; we show thousands of these warnings every month, even if we have blocked the specific attempt.
We also send alerts to G Suite administrators if someone in their corporate network may have been the target of government-backed phishing. And we regularly post public advisories to make sure that people are aware of this risk.
This is what an account warning looks like; an extremely small fraction of users will ever see one of these, but if you receive this warning from us, it's important to take immediate action on it.
We hope you never receive this type of warning, but if you do, please take action right away to enhance the security of your accounts.
Even if you don’t receive such a warning, you should enable 2-step verification in Gmail. And if you think you’re at particular risk of government-backed phishing, consider enrolling in the Advanced Protection Program, which provides even stronger levels of security.