For many years, Google offered an optional "sign in" feature for Chrome, which presumably collected your browsing data and shipped it off to Google. But that was an option that could be ignored, meaning you had the option to keep your browsing data on your computer.
But with the latest update to Chrome, this sign-in experience changed.
From now on, every time you log into a Google property (for example, Gmail), Chrome will automatically sign the browser into your Google account for you. It'll do this without asking, or even explicitly notifying you.
Matthew Green, a cryptographer and professor at Johns Hopkins University, says that the change "has enormous implications for user privacy and trust."
According to Google, the new feature that triggers this auto-login behavior has been added in the browser because of shared computers/browsers. When one or more users would be using the same Chrome browser, data from one or more users would accidentally be sent to another person's Google account.