There are tons of free CMS available today including WordPress, Drupal and Joomla. Though most of these are free, a webmaster who uses them has to constantly keep upgrading the software to make use of new features and plug security holes.
Upgrading is always a pain, one of the reasons we are coming out with WordPress Remote Manager shortly. In addition to that, Google Webmasters Tools has decided to introduce a new feature where they will alert users whenever their web software is out of date.
One of the ways we identify sites to notify is by parsing source code of web pages that we crawl. For example, WordPress and other CMS applications include a generator meta tag that specifies the version number. This has proven to be tremendously helpful in our efforts to notify webmasters. So if you’re a software developer, and would like us to help you notify your users about newer versions of your software, a great way to start would be to include a generator meta tag that tells the version number of your software. If you’re a plugin or a widget developer, including a version number in the source you provide to your users is a great way to help too.
Google Webmaster Tools basically rely on the version numbers included in the HTML source of a webpage to identify if a website requires and upgrade. However, there have been known cases of people attacking a website because of including the version number in the page. It is always better to rely on your own process to keep your software and plugins up-to-date.
This initiative will definitely help many users who usually do not have time or are unaware about new versions and will complement Google’s role on alerting users whenever their website is hacked or compromised.
New software version’ notifications for your site [Official Google Webmaster Blog]