Host your own zkBox
When total security is required, you can have your own zkBox installation.
This can be a solution if your organization's policy is not accepting that the data is processed by other companies, if you'd like to have complete control over your data or if the data should be physically located within the perimeter of your organization.
This freedom is coming with a price: you'll have to install and maintain your zkBox installation.
Using the AWS as backend
zkBox can be configured to use Amazon Web Services as backed for your data.
If it's feasible for you to deploy your zkBox instance in the Amazon cloud then it will make a lot of sense to have it configured with AWS as backend. This will save you from the burden task of taking care of the data, so it will dramatically reduce your maintenance costs.
You will simply have one or more zkBox instances running on EC2 nodes dedicated only to you. You have complete control over them and over the data stored in the Amazon cloud.
Using SQL Server as backend
If it's not acceptable to store the data outside the perimeter of your company, then you might think of using Microsoft SQL Server as storage backend for your zkBox data.
In this way you can comply with the highest security demands. You'll be able to have all your sensitive data physically hosted at your premises and complying fully with your security policy.
Requirements: SQL Server 2008, IIS7, Windows Server 2008