The Justice Department on Tuesday announced the dismantling of a global network of computers infected by malware that Russia's state security services have allegedly used for nearly 20 years to steal secrets from the U.S. and NATO allies.

The operation -- code named "MEDUSA" -- aimed to neutralize the so-called "Snake" malware used by a unit within the Russian FSB known as "Turla," which experts consider to be of the most sophisticated cyber espionage groups in the world.

DOJ and other global partners identified the Snake malware in computer systems in at least 50 countries that officials said the Turla group used to target NATO member states, financial sectors, journalists and other targets of the Russian government dating back as early as 2004.

This is a developing story. Check back for updates.