The data you store on Tangerine's server is encrypted and backed up daily. Beyond this, your data's level of security in part depends on to whom you have provided access to your Tangerine server's account.
The security of your data prior to its being stored on Tangerine's server is a separate issue and will vary by user. As Tangerine can be used to collect data while a device is offline, in some cases you may have considerable quantities of data stored on your tablets before it is transmitted to the Tangerine server. In such cases, the data stored on tablets is only encrypted if you have activated encryption on your tablet (this is not a Tangerine setting, but a configuration often found in the tablet's operating system settings). Even for data stored on unencrypted tablets, it would be extremely difficult for someone to extract your tablet's data and make a meaningful interpretation from it.