The disclosed computer-implemented method for detecting suspicious Internet addresses may include (1) monitoring Internet communications of an entity (e.g., an organization or individual), (2) compiling an Internet-address history for the entity that includes one or more Internet addresses involved in the Internet communications of the entity, (3) detecting, after compiling the Internet-address history for the entity, an additional Internet address that may be used in future Internet communications involving the entity, (4) computing a similarity metric between the additional Internet address and at least one Internet-address in the Internet-address history, (5) determining that the similarity metric indicates that the additional Internet address is suspicious, and (6) performing a security action in response to determining that the similarity metric indicates that the additional Internet address is suspicious. Various other methods, systems, and computer-readable media are also disclosed.