This applies to Oracle 9 and below. If you get an ORA-00600 in your alert log and the first and only argument which follows is , this may well have been caused by somebody typing the word oracle at the command prompt. Here is one I created earlier:
ORA-00600: internal error code, arguments: , , , , , , , 
This only happens if the database is open at the time. The message appears to go to the alert log of the database in the $ORACLE_SID.