Kaspersky noted that of the more than 60 attack groups it was tracking in cyberspace, the so-called Equation Group “surpasses anything known in terms of complexity and sophistication of techniques, and that has been active for almost two decades.”

Kaspersky Lab was founded by Eugene Kaspersky, who studied cryptography at a high school co-sponsored by the K.G.B. and once worked for the Russian military. Its studies, including one describing a cyberattack of more than 100 banks and other financial institutions in 30 countries, are considered credible by Western experts.

The fact that security software made by Kaspersky Lab is not used by many American government agencies has made it more trusted by other governments, like those of Iran and Russia, whose systems are closely watched by United States intelligence agencies. That gives Kaspersky a front-row seat to America’s digital espionage operations.