The remote host is vulnerable to multiple attack vectors.
The version of WordPress installed on the remote host fails to sanitize the 'sourceURI' before passing it to the 'wp_remote_fopen()' function when processing pingbacks. An unauthenticated remote attacker can leverage this issue to determine the existence of local files and possibly even to view parts of those files, subject to the permissions of the web server user ID. In addition, the version is also reportedly susceptible to a denial of service attack because it allows an anonymous attacker to cause a server to fetch arbitrary URLs without limits.
Upgrade to WordPress 2.1, or later.