"Google Chrome checks for updates every five hours. It is using the recently open sourced Google update component code-named Omaha, which keeps polling for updates even when Google Chrome is not running. (...) Once a new update is found to be available on the server, the client automatically downloads and installs it in the background without prompting the user. The new version of Google Chrome gets applied at the next restart of the browser. At the time of this writing, in April 2009, the user was not even prompted to restart the browser after a new update was ready. Given that the whole update process happens without any user interruption, Google Chrome is said to have a "silent update" mechanism. As of April 2009, the user could not disable update checks."
Other browsers don't include auto-updating mechanisms (Opera) or they have updating features that require user's consent (Firefox). Internet Explorer wasn't included in the report because its user-agent omits the minor version number and the results were compiled from Google's traffic logs.
Roger Halbheer, who works for Microsoft, has a more balanced view. "Silently installing components without even giving me the option to choose is not acceptable today for me – but I want to have the option to do it if I want."
Google Updater, the software that automatically updates Google applications like Chrome, Google Earth Plugin or Google Gears, needs to be more transparent and more flexible. Users need to be informed more clearly that the software updates silently and they need to have an option that disables the updater or makes the polling less frequent. What happens if the latest version of Google Chrome constantly crashes on your computer? You could install an older version, but Chrome will automatically update to the most recent version.