TNS listener can be shutdown by any user if the server is not protected with a password. This signature indicates a possible attempt at sending a STOP command to the TNS listener. This can be done with the lsnrctl command, the tnscmd perl script or via tnsnames.ora.
Oracle Oracle9i 188.8.131.52
Denial of Service
Oracle has released a Critical Patch Update. Please visit Oracle Critical Patch Update site and apply the appropriate patches.