The Grum botnet, which had control servers based predominantly in Panama, Russia and Ukraine, is believed to have been behind around one-fifth of all junk emails.
Local internet service providers (ISPs) teamed up with security company FireEye and spam-tracking service SpamHaus to clamp down on the network.
"Grum's takedown resulted from the efforts of many individuals," said FireEye security researcher Atif Mushtaq.
"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."
The operation began at the start of this week when a Grum server in Holland was taken out, followed by command and control servers in Panama.
Researchers were then able to pinpoint the location of secondary servers in the Ukraine, which has been considered a safe haven for spambots in the past.
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Mushtaq added: "There are no longer any safe havens. Most of the spam botnets that used to keep their CnCs in the USA and Europe have moved to countries like Panama, Russia, and Ukraine thinking that no-one can touch them in these comfort zones.
"We have proven them wrong this time. Keep on dreaming of a junk-free inbox."