Great question. We should add it to a FAQ. The PCI-DSS rules apply to systems that store the entire credit card number ("PAN" in PCI-DSS parlance). We don't accept the full credit card number -- just the first six digits (which identify the type of credit card and bank) and the last four (typically printed on receipts), which the PCI-DSS rules allow for. So if you're PCI compliant already, you'll still be PCI compliant if you use Sift Science.