Organizations' security professionals should understand how each department works; create flow charts of individual business functions or processes, and review all documents associated with the processes to identify fraud opportunities; and implement countermeasures or strengthen measures already in place. Essential controls include an accounting system audit trail, segregation of duties, independent checks and balances, and physical security measures. The controls and procedures must be enforced and audited periodically to ensure that they are not being ignored. Types of corporate fraud include phony invoicing, payroll fraud, receiving dock fraud, merchandise shipments to fictitious customers, contractors billing for work not done or done with inferior materials, and fleet fraud in vehicle maintenance shops.