Index: wp-includes/user.php
===================================================================
--- wp-includes/user.php	(revision 17358)
+++ wp-includes/user.php	(working copy)
@@ -489,6 +489,8 @@
 			else
 				$search_columns = array('user_login', 'user_nicename');
 
+			$search_columns = apply_filters('user_search_columns', $search_columns, $search);
+
 			$this->query_where .= $this->get_search_sql( $search, $search_columns, $wild );
 		}