« From March to December 2012 we used [...] a distributed port scanner to scan all IPv4 addresses. These scans include service probes for the most common ports, ICMP ping, reverse DNS and SYN scans. We analyzed some of the data to get an estimation of the IP address usage. »
« All data gathered during our research is released into the public domain for further study. The full 9 TB dataset has been compressed to 565GB using ZPAQ and is available via BitTorrent. »
The original message: ►http://seclists.org/fulldisclosure/2013/Mar/166
A good explanation: ▻http://www.zdnet.com/illegal-botnet-census-finds-1-2m-devices-with-default-passwords-7000012871
Do note that the machines which scanned were cracked machines and so the entire operation was probably illegal in most countries.