WordPress at a glance
filter is not described

pingback_useragent filter-hook . WP 2.9.0

Filters the user agent sent when pinging-back a URL.

Usage

add_filter( 'pingback_useragent', 'filter_function_name_7754', 10, 5 );
function filter_function_name_7754( $concat_useragent, $useragent, $pingback_server_url, $pagelinkedto, $pagelinkedfrom ){
	// filter...

	return $concat_useragent;
}
$concat_useragent(string)
The user agent concatenated with ' -- WordPress/' and the WordPress version.
$useragent(string)
The useragent.
$pingback_server_url(string)
The server URL being linked to.
$pagelinkedto(string)
URL of page linked to.
$pagelinkedfrom(string)
URL of page linked from.

Where the hook is called

pingback()
wp-includes/comment.php 2668
$client->useragent = apply_filters( 'pingback_useragent', $client->useragent . ' -- WordPress/' . get_bloginfo( 'version' ), $client->useragent, $pingback_server_url, $pagelinkedto, $pagelinkedfrom );

Where the hook is used (in WP core)

Does not used.