Problem: You have a database of links that you've collected over couple years, however, some of the links in the database do not exists anymore and when clicked show up with a 404 error.

Answer: PHP is advanced enough and has a function called fsockopen(). This function will connect to the host and port we provide - that is, if the host still exists. 

In the following example, we are checking that Zonehacks.com still exists.  If the connection fails, we will let the user know.

<?php /* fsockopen returns false if the connection to the host fails. The @ infront of the method simply silences any errors. */ $bExists = @fsockopen("www.zonehacks.com", // The website to check. 80, // 80 is standard port for websites. $errno, // If provided, holds the system level error number that occurred in the system-level connect() call. $errstr, // The error message as a string. 30); // The connection timeout, in seconds. /* If the site exists, show it off proudly */ if($bExists) { echo "<a href=\"http://www.zonehacks.com\">ZoneHacks</a>"; } else { echo "<a href=\"http://www.zonehacks.com\">ZoneHacks Dead!! :(</a>"; } ?>

Simple. =)