When multiple Wireless Access Points (WAPs) are using similar frequencies with high power settings, it can cause channel overlap, leading to interference and connectivity issues. This is likely the reason why mobile users are unable to access the internet in the lobby. Evaluating and adjusting the channel settings on the WAPs to avoid overlap is crucial to resolving the connectivity problems.

The file left by the external vendor, containing detailed architecture information and code snippets, is best described as proprietary data. Proprietary data is information that is owned by a company and is essential to its competitive advantage. It includes sensitive business information such as trade secrets, intellectual property, and confidential data that should be protected from unauthorized access.

Geographic dispersion is the practice of having backup data stored in different locations that are far enough apart to minimize the risk of a single natural disaster affecting both sites. This ensures that the company can recover its regulated data in case of a disaster at the primary site. Platform diversity, hot site, and load balancing are not directly related to the protection of backup data from natural disasters.

Access control lists (ACLs) are rules that specify which users or groups can access which resources on a file server. They can help restrict access to confidential data by granting or denying permissions based on the identity or role of the user. In this case, the administrator can use ACLs to quickly modify the access rights of the users and prevent them from accessing the data they are not authorized to see.