scott@9i > declare
  2  cursor c1 is select username from dba_users where username in ('OLD','NEW');
  3  begin
  4  for mag in c1 loop
  5  execute immediate ('alter user '||mag.username||' password expire');
  6  end loop;
  7  end;
  8  /

PL/SQL procedure successfully completed.

scott@9i > connect old/old
ERROR:
ORA-28001: the password has expired


Changing password for old
New password:
Retype new password:
ERROR:
ORA-00988: missing or invalid password(s)


Password unchanged
Warning: You are no longer connected to ORACLE.