Index: wp-includes/comment.php
===================================================================
--- wp-includes/comment.php	(revision 16692)
+++ wp-includes/comment.php	(working copy)
@@ -351,7 +351,7 @@
 		foreach ( $cols as $col )
 			$searches[] = "$col LIKE '%$string%'";
 
-		return ' AND (' . implode(' OR ', $searches) . ')';
+		return apply_filters_ref_array( 'comment_search_sql', array(' AND (' . implode(' OR ', $searches) . ')', $string, $cols, $searches ) );
 	}
 }
 
Index: wp-includes/user.php
===================================================================
--- wp-includes/user.php	(revision 16692)
+++ wp-includes/user.php	(working copy)
@@ -549,7 +549,7 @@
 				$searches[] = "$col LIKE '$string$wild_char'";
 		}
 
-		return ' AND (' . implode(' OR ', $searches) . ')';
+		return apply_filters_ref_array( 'user_search_sql', array(' AND (' . implode(' OR ', $searches) . ')', $string, $cols, $searches ) );
 	}
 
 	/**