Forget about bad apples and personal grudges. A recent international study by the American Management Association found that trying to meet impossible goals set by business owners and managers was the number one reason employees lie, cheat, and steal.

Getting a career boost or simply protecting one's livelihood came in second and third, while a personal desire to do outright damage to an employer was second to last, the study found.

In fact, many of the roots of unethical corporate behavior identified in the study, which surveyed some 1,121 managers and HR experts worldwide, are eerily similar to the sorts of upstanding values recruiters look for in a good employee -- willingness to follow orders, be a team player, and help the company grow. Yet, in an environment that doesn't foster ethical values, the study said, even well-meaning workers can go bad.

The key, according to AMA president Edward Reilly, is leadership. "Corporate leaders need to communicate ethical values throughout the organization, but they must do more than talk the talk in order to establish and sustain an ethical culture," Reilly said. That means keeping promises, encouraging open communications, keeping employees informed, and posting a formal ethical code, the study showed.

But should all businesses, big and small, have an official code of conduct?