This update is a fix for a vulnerability that was recently discovered in PHP's openssl_x509_parse() function (CVE-2013-6420).  The problem affects all versions of PHP (5.2, 5.3 and 5.4).   Customers who may be using this function to load untrusted (remote) certificates should upgrade as soon as possible. 
Linux users who wish to update can use their system update manager to obtain the new updates.
Windows and IBM i users can download the updates from the Zend Server downloads page.