Symantec believes that the attacks are aimed at sub-contractors because the attackers find them easier to exploit. After infecting Windows PCs there, the hackers use them to forge a beachhead in companies further up the supply chain.
The Elderwood gang specializes in finding and exploiting zero-days in Microsoft's IE browser and Adobe's Flash Player.
Cox called the group one of the "more elite" hacker teams, and even cited what she called their "professionalism."
"The manner in which they've structure the work, dividing it among themselves, shows a certain professionalism," Cox said. "They have a development platform in place, so they just need to pull all these components together to launch a new attack. With the group's sophistication, they can quickly and easily pull together a new attack."
This year, for example, the Elderwood group shifted gears several times, quickly returning to the attack with an exploit of a new zero-day each time its predecessor was sniffed out by security researchers.
"This year, they used a Flash zero-day in April, then a couple of weeks later one in IE, then two or three weeks after that, another, one after the other," said Cox.
Some of the zero-days attributed to Elderwood have been among the highest-profile bugs uncovered and patched this year. The vulnerability exploited by Elderwood in late May, CVE-2012-1889, was in Microsoft XML Core Services (MSXML). Attacks circulated widely enough that other security firms noticed, prodding Microsoft to patch the vulnerability in its July security update slate.
The speed with which the hackers regroup after the patching of a vulnerability told Cox that they were extremely skilled. "I would suspect, based on the speed of their attacks, that they have some sort of stockpile of zero-days," he said. "I have to assume that they have more in their arsenal than we've found."
As always when researchers pull aside the curtain on a hard-working hacker gang, the immediate assumption by many is that the attackers are backed by a government. That's not necessarily the case, according to Cox, who said Symantec had no hard evidence.
"But this is a full-time job," she said, and requires a large team to dig up vulnerabilities, build exploits, bundle them into malware, launch attacks and then digest the information they've stolen. "The work they do is both skilled and time consuming. They would have to work at it full time, so someone is paying them to do this."
She said it's likely that the group is working on a contractual basis, and attacking targets identified for them by their backer. "The analysis has shown that certain organizations have been hit in different ways, indicating that they're of particular interest to [their paymasters]," Cox added.
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