A 404 page is what a user sees when they try to reach a non-existent page on a site (because they've clicked on a broken link, the page has been deleted or they've mistyped a URL).
While the standard 404 page can vary depending on your web host, it doesn't usually provide the user with much useful information and users may just surf away from your site. Therefore, Google recommend creating a custom 404 page that provides the user with more information about the site and its content.
The Google 404 widget is a quick and easy way to embed a search box on a custom 404 page and provide users with useful information designed to help them find the information they need.
Where it can, the Google widget will also suggest other ways for the user to find the information they need, thus increasing the likelihood that they'll continue to explore your site.
A Google webmaster account is needed.
Also submit an XML sitemap of the blog to ensure the Google 404 widget works effectively.
Unpack and upload it to the /wp-content/plugins/ directory.
Activate the plugin through the 'Plugins' menu in WordPress.
· WordPress 2.5 or higher
What's New in This Release: [ read full changelog ]
· Added documentation to readme file.