Many companies, such as Wal-Mart, store much of their business and customer data in large databases called data warehouses. Their customers are not told the extent of the information accumulated on them, how long it will be kept, nor the uses to which it will be put (Hays, 2004). This data is subsequently analyzed to produce new information to help the companies evaluate business processes and customer behavior. Data mining is usually used to do the analysis. Much of the mined data is public or semi-public what we purchase at the supermarket, where we surf the Web, where we work, our salary.