Clarify that port forwarding will not be enabled until the user has

authenticated.

[originally from svn r1479]

doc/using.but

@@ -1,4 +1,4 @@
-\versionid $Id: using.but,v 1.3 2001/12/06 20:05:39 simon Exp $
+\versionid $Id: using.but,v 1.4 2001/12/13 17:38:59 simon Exp $
 
 \C{using} Using PuTTY
 
@@ -266,9 +266,12 @@ box. Enter the destination host name and port number into the
 \b Now click the \q{Add} button. The details of your port forwarding
 should appear in the list box.
 
-Now start your session. To check that PuTTY has set up the port
-forwarding correctly, you can look at the PuTTY Event Log (see
-\k{using-eventlog}). It should say something like this:
+Now start your session and log in. (Port forwarding will not be
+enabled until after you have logged in; otherwise it would be easy
+to perform completely anonymous network attacks, and gain access to
+anyone's virtual private network). To check that PuTTY has set up
+the port forwarding correctly, you can look at the PuTTY Event Log
+(see \k{using-eventlog}). It should say something like this:
 
 \c 2001-12-05 17:22:10 Local port 3110 forwarding to
 \c          popserver.example.com:110