Source confidentiality is the duty to protect the identities and communications of people who share information privately. In cyber security, it matters because a breach does not need to expose every message to cause harm. Access to an email account, chat archive, file store, or even metadata can reveal who contacted whom, when, and about what. That can put whistleblowers, informants, journalists, and other sensitive contacts at risk.
Attackers often target source confidentiality through phishing, account takeover, malware, or cloud compromise. They may read mailboxes, steal attachments, or reconstruct relationship networks from contact lists and message history. Defenders reduce that risk with multi-factor authentication, strong access control, encryption, short retention periods, logging, and careful separation of sensitive communications from routine traffic. The goal is not only to protect content, but also to keep trust boundaries intact.