Default SQL Trace is enabled in SQL Server by default to capture many useful information listed below:
http://blogs.technet.com/vipulshah/archive/2007/04/16/default-trace-in-sql-server-2005.aspxTo capture all this information, it should / would ideally use the sa privileges and hence it is configured to run using sa credentials.
We have the option to either disable it but not change the default user for it.
Steps to disable the trace( Not recommended):
sp_configure 'default trace enabled' , 0
GO
RECONFIGURE WITH OVERRIDE
GO