In 1987, Stern showed how the parameters for secret truncated linear congruential generators could be derived in polynomial time. Here, we present a modification to that algorithm which makes it simpler, more robust, and require less data. We then present a more careful analysis of the algorithm, and establish some limits of its applicability. Thus, secret truncated linear congruential generators may not necessarily be insecure for properly chosen parameters. Unfortunately, as in the original algorithm, all the results remain heuristic, however we present results of numerical experiments which support our conclusions.