Google on Thursday said that starting in January, only extensions offered through its own e-market can be installed on the Windows version of Chrome.
The move will be one more in a series of steps that Google has taken in the last 15 months to lock down the browser, pushing it and its add-ons toward the closed markets modeled by Apple's and Microsoft's mobile app environments.
Erik Kay, director of Chrome engineering, announced the change on the Chromium blog, saying that it was driven by "our continuing security efforts," and adding, "We believe this change will help those whose browser has been compromised by unwanted extensions.
Google has used similar explanations for previous steps to bar extensions from the browser.
At some point in early 2014, users of the "Stable" and "Beta" builds of Chrome on Windows will be able to install extensions -- what other browser makers call "add-ons" -- only from the Chrome Web Store, Google's official distribution channel.
Currently, some extensions not hosted on the Chrome Web Store can still be installed in the browser, including those associated with a desktop application -- and offered during the installation process of that program -- and ones written by a business for its workers. Generically, Google calls them "external extensions."
But Google has been clamping down on what it has viewed as rogue extensions since July 2012, when it first required that add-ons move to the Chrome Web Store. As of Chrome 21, which launched that month, the browser would not accept extensions installed directly from websites, but only from the Chrome Web Store. Before that, any website could prompt a Chrome user to install an add-on.
Then in February 2013 Google tightened its policies when it debuted a new security feature that blocked silent installations of add-ons and disabled those that had snuck into the browser.
Silent extension installation had been possible only on Windows; OS X and Linux did not offer slippery websites a way to sneak an add-on into Chrome.
Apparently, those moves weren't enough for Google.
"Many services bundle useful companion extensions, which causes Chrome to ask whether you want to install them (or not)," wrote Kay yesterday. "However, bad actors have abused this mechanism, bypassing the prompt to silently install malicious extensions that override browser settings and alter the user experience in undesired ways."
That prompted the company's more draconian move to require every extension to be hosted on the Chrome Web Store, so that Google can vet the software and, if necessary, yank the add-on if it turned out to be malicious.
Starting in January, extensions that had been installed locally or by businesses internally must be published to the Chrome Web Store, closing the remaining loopholes on Windows. Businesses can hide their extensions on the store from the public at large -- or continue to use group policies to offer the add-ons to their workforce from their own servers -- and developers will still be able to initiate "in-line" installs from their website, assuming the add-on is in the Chrome Web Store.
The move was not completely unexpected. In a May 2012 thread discussing the changes planned for Chrome 21, a Chromium developer noted that, "Our hope and belief is that this installation mechanism will be sufficiently complex that it will reduce the number of off-store extension installs performed. If it doesn't help, we'll try something else."
The new rules will not affect the "Dev" build of Chrome, the roughest-edged version, or "Canary," an even less-polished browser from the Chromium project, the open-source foundation of Chrome. Web apps will not be affected by the policy change.
Google did not specify which version of Chrome will be the first to require all extensions to originate from the browser's store, but by the company's usual tempo, it will likely be Chrome 33.
As of Friday, Chrome Stable was at version 30, and Beta was at version 31.
Browser extensions can be found at the Chrome Web Store.
Gregg Keizer covers Microsoft, security issues, Apple, Web browsers and general technology breaking news for Computerworld. Follow Gregg on Twitter at @gkeizer, or subscribe to Gregg's RSS feed . His email address is email@example.com.