Grum's control servers were mainly based in Panama, Russia and Ukraine.
Security company FireEye and spam-tracking service SpamHaus worked with local internet service providers (ISPs) to shut down the illegal network.
A botnet is a network of computers that has been hijacked by cybercriminals, usually by using malware.
"Grum's takedown resulted from the efforts of many individuals," wrote Atif Mushtaq, a security researcher with FireEye.
"This collaboration is sending a strong message to all the spammers: Stop sending us spam. We don't need your cheap Viagra or fake Rolex."
Major spam botnet taken out
Posted on Friday, July 20 2012 @ 12:49 CEST by Thomas De Maesschalck
BBC News reports security researchers shut down Grum, a botnet thought to be responsible for 18 percent of world's spam e-mail.