Setting the hidden parameter _trace_files_public to true sets the file protections so that non-Oracle users can read the trace files. While it is unlikely that general users have access to the database server, best practices requires that this parameter be set to the default value of false.
Trace files can often contain proprietary company information such as schema information or passwords, as well as personal information such as phone numbers and social security numbers that are used in retrievals.
To alter this setting use the
alter system set trace_files_public=false scope=both;