It has recently been proved by Nguyen and Shparlinski that the Digital Signature Algorithm (DSA) is insecure when a few consecutive bits of the random nonces k are known for a reasonably small number of DSA signatures. This result confirmed the efficiency of some heuristic lattice attacks designed and numerically verified by Howgrave-Graham and Smart. Here, we extend the attack to the Nyberg-Rueppel variants of DSA. We use a connection with the hidden number problem introduced by Boneh and Venkatesan and new bounds of exponential sums which might be of independent interest.