diff -r bd4f5052a532 -r 112a04c0473d _exceptions.py
--- a/_exceptions.py	Fri Nov 16 11:53:17 2012 +0100
+++ b/_exceptions.py	Mon Dec 03 00:03:03 2012 +0100
@@ -103,6 +103,10 @@
         except Exception, ex:
             return str(ex)
 
+class Forbidden(SecurityError):
+    """raised when a user tries to perform a forbidden action
+    """
+
 # source exceptions ###########################################################
 
 class EidNotInSource(SourceException):