Globally identified users

Oracle database 11.2.0.3 Std Edition One

Database is a 'data warehouse' storing historical sales, product, and customer information.  A small handfull of "power users" have their own user accounts and access the db via an ODBC connection into Excel.

The problem is that Bob will develop a spreadsheet with a connection definition, then share it around.  And the connection definition in the workbook contains his connection credentials, including password in clear text.  This results in users, at the least, unknowingly connecting using someone else's credentials, and at the worst actually discovering someone else's credentials and propogating that use elsewhere.  My daily audit report shows a dozen or so connections per day where someone is using someone else's credentials.