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 fingerprint – can 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.