A week ago, a half-million bot-infected machines were freed from their “master” botnet servers. Many of these bots were members of the world’s most prolific spam botnets, Srizbi, Mega-D and Rustock “– likely still spamming away for other botnets. The Shadowserver Foundation, a volunteer organization that gathers intelligence on the Internet’s dark side, is building a so-called “sinkhole” server that poses as a defunct malicious domain server to find out what these machines leave behind.”]
Source: https://www.darkreading.com/attacks-breaches/orphaned-bots-not-necessarily-free-or-clean