diff -ruN /home/dan/moodle/moodle/lib/filelib.php moodle/lib/filelib.php
--- /home/dan/moodle/moodle/lib/filelib.php	2007-12-29 20:36:51.000000000 +0000
+++ moodle/lib/filelib.php	2007-12-30 01:16:01.000000000 +0000
@@ -214,6 +214,11 @@
 function mimeinfo($element, $filename) {
     static $mimeinfo;
     $mimeinfo=get_mimetypes_array();
+     
+    if( preg_match('@^https?://[^/]+/?$@', $filename) ){
+        // prevent things like http://website.au returning audio/au
+        return $mimeinfo['xxx'][$element];   // By default
+    }
 
     if (eregi('\.([a-z0-9]+)$', $filename, $match)) {
         if (isset($mimeinfo[strtolower($match[1])][$element])) {
diff -ruN /home/dan/moodle/moodle/lib/simpletest/testfilelib.php moodle/lib/simpletest/testfilelib.php
--- /home/dan/moodle/moodle/lib/simpletest/testfilelib.php	1970-01-01 01:00:00.000000000 +0100
+++ moodle/lib/simpletest/testfilelib.php	2007-12-30 01:18:54.000000000 +0000
@@ -0,0 +1,34 @@
+<?php
+/**
+ * Unit tests for (some of) ../filelib.php.
+ */
+
+if (!defined('MOODLE_INTERNAL')) {
+    die('Direct access to this script is forbidden.');    ///  It must be included from a Moodle page
+}
+
+class filelib_test extends UnitTestCase {
+
+    function setUp() {
+
+    }
+
+    function tearDown() {
+
+    }
+
+    function test_mimeinfo() {
+        // .au and audio, see MDL-3674
+        $this->assertNotEqual('audio/au', mimeinfo('type', 'http://test.au/') );
+        $this->assertNotEqual('audio/au', mimeinfo('type', 'http://test.au') );
+        $this->assertNotEqual('audio/au', mimeinfo('type', 'http://www.test.au/') );
+        $this->assertNotEqual('audio/au', mimeinfo('type', 'http://a.au/') );
+        $this->assertEqual('audio/au', mimeinfo('type', 'http://test.au/x.au') );
+        $this->assertEqual('audio/au', mimeinfo('type', 'http://test.au/a/very/long/sub/directory/and.au') );
+        $this->assertEqual('audio/au', mimeinfo('type', 'file://test.au') );
+        $this->assertEqual('audio/au', mimeinfo('type', '../test.au') );
+        $this->assertEqual('audio/au', mimeinfo('type', 'test.au') );
+
+    }    
+}
+?>