Google is working on blocking tab-under behavior in Chrome, according to a document seen by Bleeping Computer.

For users unfamiliar with the jargon, Google considers tab-under behavior when an unsuspecting user is scrolling or clicking on a page, but the site duplicates the current page in another tab and shows an ad or a new website in the page the user was initially reading.

This demo site created by Google engineers shows how tab-unders work.

Tab-unders abused to show ads, redirect users to other sites

Countless of website owners and advertisers have abused tab-unders to show ads and redirect users to unwanted sites, all for the sake of ad impressions and redirection fees.

Telemetry gathered by Google showed that a big percentage of the original pages (now showing ads or another website) are never engaged with again, meaning they're obviously abused to spam users.

Google engineers have grown tired of this behavior and started working on a way to address tab-unders last year in November.

Chrome will block and show an alert when tab-under is detected

Earlier today, Google published a document detailing three ways it's currently looking at for dealing with tab-unders in Chrome.

The first and second proposals are to use the existing Chrome framebusting detection framework to show an alert inside the page. The warning would look like so:

Chrome tab-under UI blocking UI

The difference between the two is that the first proposal recommends showing the warning on the original page before a new tab is created, while the second argues that Chrome should close the original tab immediately and show the warning on the new page.

Chrome engineers are currently favoring the first, as the second would mean to allow for the creation of a new tab that doesn't necessarily hold the previous page's navigational history, breaking the Back button.

A third suggestion was also proposed to improve the existing Chrome pop-up blocker and add support for tab-unders, but the first proposal won out.

Tab-under blocking will arrive in Chrome Canary first

The document is marked as  "Intent to Implement," meaning it will soon make its way into Chrome dev builds.

According to Chrome engineer Charles Harrison, the tab-under blocking feature will be supported on five of the six Blink platforms — Windows, Mac, Linux, Chrome OS, and Android, but not Android WebView.

Once the feature is ready, it will ship with Chrome Canary under its own option on the chrome://flags settings page. There's no information available on the Chrome version number this feature will arrive for early testing.