Are bribes and "grease" payments a necessary part of doing business abroad and what can be done to lessen the risk

For many large, global companies that do business in emerging market countries, the risk of corruption is a part of everyday life.  There may be a belief that without bribing public officials in those countries, these companies could never build a factory, hire employees, get permission to build infrastructure, sell their products, or conduct other business functions.  Shipping merchandise and other items in or out of these countries can be equally difficult, with customs agents in these countries demanding unofficial or “grease” payments to allow shipments to be made.

Are bribes and “grease” payments a necessary part of doing business abroad and what can be done to lessen the risk?