"Confidential Information" is whatever the Confidentiality Agreement defines it as
If the agreement doesn't define it then what does it mean? A good confidentially agreement will be explicit about what is confidential, at least, it should identify classes of things that are confidential. Client lists can be confidential or not - if you aren't told, how would you know?
There is an equitable remedy of breach of confidence and the court may look to the definition that uses:
The most generally accepted statement of a breach of confidence claim, by Megarry J in Coco v Clark (Engineers) Ltd  RPC 41 at 47-48; 1A IPR 587, is that the following matters must be established:
- First, that the information has the necessary quality of confidence.
- Secondly, that the information was imparted to the defendant in circumstances importing an obligation of confidence.
- Thirdly, that the defendant used the information without the authority of the plaintiff and to its detriment.
The "necessary quality of confidence" requires that the plaintiff takes the necessary and prudent steps to keep it secret; public information is never confidential1, however, that alone is insufficient. Not every secret attracts protection, it must also by its nature warrant confidentiality. The fact that the plaintiff has a business relationship with McDonalds is unlikely to meet that requirement while the specific contract terms and even the name of the plaintiff's point of contact with McDonalds might. A list of clients is not ipso facto a "client list" worthy of confidentiality.
How the plaintiff disclosed the information must make it clear that the information is confidential. Whether this happened depends on:
- the nature of the information,
- the purpose of the transfer of the information,
- the limits the confider placed on the use of the information.
Where the information that McDonalds was a customer was simply transferred with no restriction, its hard to see that second matter has been established, particularly if the receiver disclosed the information before the retroactive attempt to make it confidential.
Finally, what damage is caused by the disclosure that McDonalds is a customer?
1 There is a divergence between English and Australian law on if subsequent public disclosure (e.g. in a patent application) releases the receiver of the information from its obligation of confidence - in England it does, in Australia it doesn't. Both jurisdictions agree that if the information was public before the disclosure happened then it never was confidential information.