Update security.rst

Author: Mathieu

book/security.rst

@@ -508,8 +508,9 @@ else, you'll want to encode their passwords. The best algorithm to use is
 .. include:: /cookbook/security/_ircmaxwell_password-compat.rst.inc
 
 Of course, your users' passwords now need to be encoded with this exact algorithm.
-For hardcoded users, you can use an `online tool`_, which will give you something
-like this:
+For hardcoded users, you can use an `online tool`_ (this is a public tool and it should not be used with real passwords because of the risk of farming or other possible security issues).
+
+It will give you something like this:
 
 .. configuration-block::