backupdata folder is not visible in directory resource any more, the backup files were not downloadable, but they might be stored in browser cache when teacher and student were logged from the same browser and computer account - MDL-6280 ; merged from MOODLE_16_STABLE

file.php

@@ -53,11 +53,12 @@
     }
 
     // security: only editing teachers can access backups
-    if ((!has_capability('moodle/site:backup', get_context_instance(CONTEXT_COURSE, $course->id)))
-        and (count($args) >= 2)
-        and (strtolower($args[1]) == 'backupdata')) {
-
-        error('Access not allowed');
+    if ((count($args) >= 2) and (strtolower($args[1]) == 'backupdata')) {
+        if (!has_capability('moodle/site:backup', get_context_instance(CONTEXT_COURSE, $course->id))) {
+            error('Access not allowed');
+        } else {
+            $lifetime = 0; //disable browser caching for backups 
+        }
     }
 
     if (is_dir($pathname)) {