But American intelligence officials said that it was unclear if the use of the malware was state-sponsored, and that Snake was just one of many types of malware that Ukraine is battling every day.

Versions of Snake’s predecessor have been around since 2005, but the highly sophisticated one found in Ukraine appears to have been directed at government agencies. The attacks were aimed mostly at siphoning data from local computers to other servers, the report said. It identified 14 cases of Snake in Ukraine since the start of 2014, compared to eight cases in the whole of 2013. In all there have been 32 reported cases in Ukraine since 2010, out of 56 worldwide.

One mystery is whether Snake is now being turned to purposes that go beyond mere espionage: manipulating or alerting computer networks in some way. Russian hackers — both those employed by the state and those working on their own — are known for their abilities to design sophisticated “implants” that both suck data out of a system and create a pathway for other malicious software to be injected. Documents stolen from the National Security Agency by Edward J. Snowden, the former N.S.A. contractor now living in Moscow and interviews with intelligence officials indicate the United States also has extensive capability to do similar things.

“The usual Russian approach would be to design something that could both conduct surveillance and aid in an attack,” said one senior intelligence official, describing how the National Security Agency and the Pentagon’s Cyber Command were on the lookout for the kind of computer attacks that were unleashed on Estonia seven years ago. The precise origins of those attacks have never been completely understood.

While some early reports about Snake compared it to Stuxnet, the American- and Israeli-designed worm that attacked Iran’s nuclear program, the inner workings of Snake appear to be quite different. Stuxnet took over the computer controllers that ran Iran’s nuclear centrifuges, spinning those centrifuges out of control. So far, there is no evidence that Snake can do that.