Russia is likely behind a long-running computer spying campaign, although the stealthy attacks leave fewer clues than other state-sponsored attacks, according to a new report from FireEye.

FireEye calls the group APT28, which is short for “advanced persistent threat,” a nomenclature the company’s Mandiant division has used to classify attacks its analysts believe come from a distinct group.

APT has been active for at least six years. It tends to focus on targets that would be of interest to Russia, such as the Caucasus region with a focus on Georgia and European governments, militaries and security organizations.

But Russian activity in cyberspace is harder to track, and FireEye’s attribution of attacks by APT28 are based an analysis of the malicious code and timing.

For example, FireEye’s report says that more than half of the malicious files it analyzed were set to Russian language settings, which suggests “that a significant portion of APT28 malware was compiled in a Russian-language build environment consistently over the course of six years.”

Also, 96 percent of the malware was compiled between a Monday and Friday during an 8 AM to 6 PM work day in the Moscow time zone.

FireEye’s Mandiant branch is well-known for describing in early 2013 what it contended was a state-sponsored hacking program run by a unit of China’s People’s Liberation Army in Shanghai in a report that included photos of the building where it allegedly operates.

In May, the U.S. Department of Justice charged five members of the People’s Liberation Army with stealing trade secrets from U.S. companies, including some of those identified by nicknames in Mandiant’s report.

With Russia, “we dont have pictures of a building, personas to reveal, or a government agency to name, what we do have is evidence of long-standing, focused operations that indicate a government sponsor specifically, a government based in Moscow,” FireEye’s report said.

APT28 targets its victims with spearphishing emails, which try to convince people to open a file or follow a link, which could result in a malware infection.

Some of the common tools that APT28 tries to install on computers include Sourface, also called Sofacy, a downloader; Eviltoss, a backdoor used for running shellcode and stealing credentials; and Chopstick, which FireEye describes as a “modular implant.”

The tools used by APT28, especially Chopstick, “demonstrate formal coding practices indicative of methodical, diligent programmers,” FireEye wrote.

Eviltoss, for example, uploads an RSA public key that encrypts stolen data. Some variants of Eviltoss send the pilfered data over SMTP (simple mail transfer protocol) in an attachment, which goes out through the victim’s mail server.

“APT28 is most likely supported by a group of developers creating tools intended for long-term use and versatility, who make an effort to obfuscate their activity,” it wrote. “This suggests that APT28 receives direct ongoing financial and other resources from a well-established organization, most likely a nation state government.”