What is the theory that security prices reflect all information, whether public or private?

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The theory that security prices reflect all information, whether public or private is known as strong-form efficiency. This means that not only do publicly available information (weak-form efficiency) and all publicly available information and analysis (semi-strong-form efficiency) affect security prices, but even insider information cannot be used to gain an advantage. In other words, all information, regardless of its source or accessibility, is already incorporated into security prices.

What Is the Theory That Security Prices Reflect All Information