How can I kill all sessions connecting to my oracle database?

I've been using something like this for a while to kill my sessions on a shared server. The first line of the 'where' can be removed to kill all non 'sys' sessions:

BEGIN
  FOR c IN (
      SELECT s.sid, s.serial#
      FROM v$session s
      WHERE (s.Osuser = 'MyUser' or s.MACHINE = 'MyNtDomain\MyMachineName')
      AND s.USERNAME <> 'SYS'
      AND s.STATUS <> 'KILLED'
  )
  LOOP
      EXECUTE IMMEDIATE 'alter system kill session ''' || c.sid || ',' || c.serial# || '''';
  END LOOP;
END;