Google analytics: le session ID est un entier 32 bits

library/Class/WebService/Analytics/Client.php

@@ -66,7 +66,7 @@ class Class_WebService_Analytics_Client {
     // (could also get unserialized from database)
 		if( !isset($session->uniqueID) || !isset($session->visitor) ) {
 			$visitor = new GoogleAnalytics\Visitor();
-			$session->uniqueID = md5(Zend_Session::getId());
+			$session->uniqueID = rand(0, 2147483647);
 		}	else {
 			$visitor = unserialize($session->visitor);
 		}