How is that data secured?

The test file paths and/or branch names can be encrypted on your CI node with a salt and later send to knapsackpro.com API. You generate the salt locally and only you can decrypt the test file paths or branch names with the salt. Here you can see how the data are encrypted.

Connection with knapsackpro.com server is via https (SSL).

Regarding payments we use the BraintreePayments.com and they store credit cards and your private information.