Protecting and securing user data has been the absolute number one priority in building this product. We went through an exhaustive third-party security audit to validate the security of our platform, which was designed and built by the same people that built Amazon.com's technology for securing credit card numbers. At every step along the way, from transmitting data over a secure connection, to encrypting user credentials from the moment they are entered, we've designed our architecture with security at the forefront. The result is bank level security, with 256 bit SSL encryption for all data.
You can read more about SigFig Security here.