A 404.php page that loads by default whenever an invalid URL is visited on blog. When a web user finds your blog and is greeted with the lovely 404 page they will most commonly just click the “Back” button on their browser and continue browsing through the other search results. If 404 page is setup correctly you can often retain that traffic.
There are few great post about customizing your 404 page which includes a bunch of suggestions for retaining that traffic. I prefer to provide useful details on my 404 pages. This code will help search engine traffic hopefully find what they are looking for:
<h1>Not Found, Error 404</h1>
<p>The page you are looking for no longer exists.</p>
<p>Perhaps you can find what you are looking for by searching the site archives!</p>
<b>Search by Page:</b>
<?php wp_list_pages(‘title_li=’); ?>
<b>Search by Month:</b>
<?php wp_get_archives(‘type=monthly’); ?>
<b>Search by Category:</b>
<?php wp_list_cats(‘sort_column=name’); ?>
Sometimes popular posts plugin helps to retain the traffic. It is depending on the type of blog and the 404 page setup.