We introduce optimizations to the ZMap network scanner that achieve a 10-fold increase in maximum scan rate. By parallelizing address generation, introducing an improved blacklisting algorithm, and using zero-copy NIC access, we drive ZMap to nearly the maximum throughput of 10 gigabit Ethernet, almost 15 million probes per second. With these changes, ZMap can comprehensively scan for a single TCP port across the entire public IPv4 address space in 4.5 minutes given adequate upstream bandwidth. We consider the implications of such rapid scanning for both defenders and attackers, and we briefly discuss a range of potential applications.