update warning on signatures

docs/source/parallel/parallel_security.txt

@@ -132,11 +132,10 b" owner, just as is common practice with a user's keys in their `.ssh` directory."
 
 .. warning::
 
-    It is important to note that the key authentication, as emphasized by the use of
-    a uuid rather than generating a key with a cryptographic library, provides a 
-    defense against *accidental* messages more than it does against malicious attacks.
-    If loopback is compromised, it would be trivial for an attacker to intercept messages
-    and deduce the key, as there is no encryption.
+    It is important to note that the signatures protect against unauthorized messages,
+    but, as there is no encryption, provide exactly no protection of data privacy.  It is
+    possible, however, to use a custom serialization scheme (via Session.packer/unpacker
+    traits) that does incorporate your own encryption scheme.