This document discusses the threats, risks, and controls related to: — systems that provide digital asset custodian services and/or exchange services to their customers (consumers and businesses) and management of security when an incident occurs; — asset information (including the signature key of the digital asset) that a custodian of digital assets manages. This document is addressed to digital asset custodians that manage signature keys associated with digital asset accounts. In such a case, certain specific recommendations apply. The following is out of scope of this document: — core security controls of blockchain and DLT systems; — business risks of digital asset custodians; — segregation of customer's assets; — governance and management issues.