Protecting confidential information is a major concern for organizations and individuals alike, who stand to suffer huge losses if private data falls into the wrong hands. Network-based information leaks pose a serious threat to confidentiality. This paper describes network-based data-leak detection (DLD) technique, the main feature of which is that the detection does not require the data owner to reveal the content of the sensitive data. Instead, only a small amount of specialized digests are needed. The technique referred to as the fuzzy fingerprintcan be used to detect accidental data leaks due to human errors or application flaws. The privacy-preserving feature of algorithms minimizes the exposure of sensitive data and enables the data owner to safely delegate the detection to others.