All client information is kept strictly confidential. I respect your privacy, and will never sell or distribute your organization's sensitive data, such as contact information, ideas for new businesses, etc. Over the years, my clients have learned to trust me to the point where many of them provide credit card numbers (so I can order services on their behalf).
Occasionally, an organization will ask that I sign a nondisclosure agreement (NDA), typically because they think their business idea is fabulous, has never been thought of before, and could be stolen or revealed by their web developer, thus ruining the business's potential. Actually, it's not an idea that makes a business successful; it's the implementation and follow-through of a set of proven ideas and best practices. The world is full of promising ideas never actualized or, less frequently, tested but shown unworkable. Almost every smart businessperson is not interested in risking resources on unproven ideas. Usually such people are already too busy with their own ideas that they think are much better. This is especially true of top web developers, who already have long lists of projects they dreamed up and want to implement. The last thing they want is to make that list even longer by adding an idea in an area in which they have no interest. (I personally have hundreds of such ideas.) Also, even if the client's idea is proven viable, by then the client is already successful, and there would be no way to protect the idea since it is public (in fact, the better the marketing of the product or service, the more people know about it). What's critical to keep secret is the customer data, not the business idea. Moreover, the best web developers have reputations to protect, which they would never jeopardize by blabbing any information shared in confidence. My reputation and honor are too important to me to ever risk through indiscretion. Lastly, if you don't trust your web developer, then no contract will protect you. Only partner with professionals who have been in the field for many years (ten years or more would be best).