Index: wp-includes/vars.php
===================================================================
--- wp-includes/vars.php	(revision 23582)
+++ wp-includes/vars.php	(working copy)
@@ -96,9 +96,17 @@
  * Whether the server software is IIS 7.X
  * @global bool $is_iis7
  */
-$is_iis7 = $is_IIS && (strpos($_SERVER['SERVER_SOFTWARE'], 'Microsoft-IIS/7.') !== false);
 
+$is_iis7 = $is_IIS && (strpos($_SERVER['SERVER_SOFTWARE'], 'Microsoft-IIS/7.') || strpos($_SERVER['SERVER_SOFTWARE'], 'Microsoft-IIS/8.') !== false);
+
 /**
+ * Returns the numeric IIS server version, false if not IIS
+ * @global float $iis_version
+ */
+$iis_version = $is_IIS ? floatval(substr($_SERVER['SERVER_SOFTWARE'], 14)) : false;
+
+
+/**
  * Test if the current browser runs on a mobile device (smart phone, tablet, etc.)
  *
  * @return bool true|false