As part of the Privacy Sandbox project, Google first announced that it would phase out Chrome’s support for third-party cookies, and then said it would phase out user-agent strings in Chrome. As an important part of the functionality of modern Web browsers, the UA string refers specifically to a piece of text that the browser sends to a Web site when it initiates a connection. It contains details about browser types, rendering engines, operating systems, and more.
(Instagram via ZDNet)
In the case of the Mozilla Firefox browser used in Windows 10, it sends the following message to the web server:
Mozilla / 5.0 (Windows NT 10.0; Win64; x64; rv:71.0) Gecko / 20100101 Firefox / 72.0
In fact, UA strings were developed as part of Netscape as early as the 1990s and continue to be used today.
For decades, websites have been implementing functional fine-tuning based on visitors’ technical specifications. But now, Google believes the mechanism has become a source of trouble.
Yoav Weiss, a Google engineer, says online advertisers have used UA strings as a way to track and identify website visits. UA sniffing not only raises compatibility issues, but also creates privacy issues.
To address these issues, Google plans to freeze the entire standard and phase out user proxy strings in Chrome.
As for the long-term plan, the company will specify all Chrome’s UA strings as generic values to avoid revealing too much information about users.
This means that a new version of Chrome, such as a phone or a new operating system version, that is released on a new platform will be recognized as a generic UA string, rather than a string for that particular platform.
In the future, websites won’t be able to tell if visitors to Chrome are running on Windows 7 or Windows 10, or if Chrome Mobile is running a Samsung Galaxy/Google Pixel smartphone.
Websites only know that users are running Chrome, and it’s not clear whether a visitor is running on a desktop, or mobile device, or on a mobile device. Here’s Google’s phase-out schedule:
Starting in mid-March 2020, Google will display a warning in the Chrome console for pages that read UA strings so that the site developer can adjust the code;
By early June 2020, the Chrome 83 version, Google will freeze the Chrome version information in the UA string and unify the version number of the operating system;
By mid-September 2020, the version of Chrome 85, Google will unify the desktop operating system in the UA string and specify it as a generic value (as will mobile devices).