Added information about pickle security and SocketHandler.

Doc/library/logging.rst

@@ -2039,6 +2039,11 @@ sends logging output to a network socket. The base class uses a TCP socket.
       Pickles the record's attribute dictionary in binary format with a length
       prefix, and returns it ready for transmission across the socket.
 
+      Note that pickles aren't completely secure. If you are concerned about
+      security, you may want to override this method to implement a more secure
+      mechanism. For example, you can sign pickles using HMAC and then verify
+      them on the receiving end, or alternatively you can disable unpickling of
+      global objects on the receiving end.
 
    .. method:: send(packet)