All the information is kept within the app itself. We don't collect any information, your Whitelist is private.
We are planning to offer sync functionality in the future. When that happens your personal information will be stored in Apple's CloudKit servers in containers available only to your devices. We will not be able to access it.
We will though be able to collect some anonymized data in order to improve the funcionality of the app for every user. This data will be related to the most used domains. When we have the full details of this functionality figured out we will update this page accordingly.
The Whitelist Team