Erlang-hyperloglog is an efficient algorithm for estimating the number of distinct elements, known as the cardinality, of large data ensembles, which are referred to here as multisets and are usually massive streams (read-once sequences). This problem has received a great deal of attention over the past two decades, finding an ever growing number of applications in networking and traffic monitoring, such as the detection of worm propagation, of network attacks (e.g., by Denial of Service), and of link-based spam on the web.