Definition
Unicode steganography is a technique for hiding text inside other text by encoding it with invisible or non-rendering code points, such as the deprecated Unicode tag-block characters, so that the payload displays as nothing to a human reader but decodes cleanly when parsed by software. It has drawn attention as a vector for smuggling hidden instructions or data past content filters and into language models, since the model still tokenizes and processes the underlying characters even though a screen shows nothing there.