Index: wp-includes/feed.php
===================================================================
--- wp-includes/feed.php	(revision 5506)
+++ wp-includes/feed.php	(working copy)
@@ -151,13 +151,13 @@
 	$home = get_bloginfo_rss('home');
 	$the_list = '';
 	foreach ( (array) $categories as $category ) {
-		$category->cat_name = convert_chars($category->cat_name);
+		$cat_name = convert_chars($category->cat_name);
 		if ( 'rdf' == $type )
-			$the_list .= "\n\t\t<dc:subject><![CDATA[$category->cat_name]]></dc:subject>\n";
+			$the_list .= "\n\t\t<dc:subject><![CDATA[$cat_name]]></dc:subject>\n";
 		if ( 'atom' == $type )
-			$the_list .= "<category scheme='$home' term='$category->cat_name' />";
+			$the_list .= sprintf( '<category scheme="%1$s" term="%2$s" />', attribute_escape( apply_filters( 'get_bloginfo_rss', get_bloginfo( 'url' ) ) ), attribute_escape( $category->cat_name ) );
 		else
-			$the_list .= "\n\t\t<category><![CDATA[$category->cat_name]]></category>\n";
+			$the_list .= "\n\t\t<category><![CDATA[$cat_name]]></category>\n";
 	}
 	return apply_filters('the_category_rss', $the_list, $type);
 }