MySQL account information is stored in the tables of the
mysql database. This database and the access
control system are discussed extensively in
Chapter 5, MySQL Server Administration, which you should consult
for additional details.
Some releases of MySQL introduce changes to the structure of the grant tables to add new privileges or features. Whenever you update to a new version of MySQL, you should update your grant tables to make sure that they have the current structure so that you can take advantage of any new capabilities. See Section 4.4.8, “mysql_upgrade — Check Tables for MySQL Upgrade”.
MySQL Enterprise. In a production environment it is always prudent to examine any changes to users' accounts. The MySQL Enterprise Monitor provides notification whenever users' privileges are altered. For more information, see http://www.mysql.com/products/enterprise/advisors.html.