From gbhackers.com
Masscan – Worlds fastest scanner can scan the entire Internet in under 6 minutes, transmitting 10 million packets per second.
Masscan is an Internet-scale port scanner, useful for large-scale surveys of the Internet, or of internal networks. While the default transmit rate is only 100 packets/second, it can optional go as fast as 25 million packets/second, a rate sufficient to scan the Internet in 3 minutes for one port.