A massive botnet (alternately known as Mega-D and Ozdok) that was once responsible for an estimated third of the world’s spam has been knocked out of commission thanks to researchers from security firm FireEye, who launched a coordinated blitz on dozens of its command and control channels. The channels were used to send new spamming instructions to the legions of zombie machines that make up the network. Almost immediately, the spam stopped, according to M86 Security blog. Last year, the email security firm estimated the botnet was the leading source of spam until some of its servers were disabled. The body blow is good news to ISPs that are forced to choke on the torrent of spam sent out by the pesky botnet. But because many email servers already deployed blacklists that filtered emails sent from IP addresses known to be used by Ozdok, end users may not notice much of a change, said Jamie Tomasello, an abuse operations manager at antispam firm Cloudmark.