Disconnecting session from an on logon trigger

I'd like to create an on logon trigger that will prevent the user from connecting in certain circumstances. I have one way of doing it which would be to issue

execute immediate ' alter system kill session 'session_id', 'serial#''  

but I can't help but wonder if there's a cleaner way to do it from within oracle instead of killing the session?      

Oracle 9.2.0.7      

Thanks,
Jay Miller      

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