Some of Wal-Mart's senior executives knew about the bribes, but did not take any effective actions ...

The Board should ensure that company policies and systems are robust and comprehensive, and that the internal controls, that ensure compliance, are operating properly. This usually involves periodic examination by internal auditors and or risk management investigators, with reports to the senior executive responsible for the activity, and to the relevant board committee. Whistleblowers are a necessary aspect of the control mechanism, so they must be encouraged, supported, and their reports reported to the relevant Board Committee. The Board must take active responsibility for the oversight of these functions  they cannot rely entirely on senior management to do their job in these areas. The relevant Board Committee should hear from the senior executive overseeing these areas quarterly and should review a summary quarterly report with access to the specific reports when called for. Reports to the Board as a whole should be made by specific committees on a quarterly basis to raise the profile, awareness and importance of these functions.