The "Comment Crew," a group of China-based hackers whose outing earlier this year in major media outlets caused a row with the U.S., have resumed their attacks against dissidents.

FireEye, a security vendor that specializes in trying to stop sophisticated attacks, has noticed attackers using a fresh set of tools and evasion techniques against some of its newer clients, which it can't name. But Rob Rachwald, director of market research for FireEye, said in an interview Monday that those clients include an organization in Taiwan and others involved in dissident activity.

The Comment Crew was known for many years by security analysts, but its attacks on The New York Times, described in an extensive report in February from vendor Mandiant, thrust them into an uncomfortable spotlight, causing tense relations between the U.S. and China.

Rachwald said it is difficult to determine if the organizations being targeted now were targeted by the Comment Crew previously, but FireEye said last month that the group didn't appear to be hitting organizations they had compromised before.

Organizations opposing Chinese government policies have frequently been targeted by hackers in what are believed to be politically motivated surveillance operations.

The Comment Crew laid low for about four months following the report, but emerging clues indicate they haven't gone away and in fact have undertaken a major re-engineering effort to continue spying. The media attention "didn't stop them, but it clearly did something to dramatically alter their operations," Rachwald said in an interview.

"If you look at it from a chronological perspective, this malware hasn't been touched for about 18 months or so," he said. "Suddenly, they took it off the market and started overhauling it fairly dramatically."

FireEye researchers Ned Moran and Nart Villeneuve described the new techniques on Monday on FireEye's blog.

Two malware samples, called Aumlib and Ixeshe, had been used by the Comment Crew but not updated since 2011. Both malware programs have now been altered to change the appearance of their network traffic, Rachwald said.

Many vendors use intrusion detection systems to spot how malware sends data back to an attacker, which helps determine if a network has been compromised. Altering the method and format for how the data is sent can trick those systems into thinking everything is fine.

In another improvement, encryption is now employed to mask certain components of the programs' networking communication, Rachwald said. The malware programs themselves, which are designed to steal data and log keystrokes, are basically the same.

Mandiant's report traced the hacking activity to a specific Chinese military unit called "61398." The company alleged that it waged a seven-year hacking spree that compromised 141 organizations.

Rachwald said it is strongly believed the Comment Crew is behind the new attacks given its previous use of Aumlib and Ixeshe. But the group has also re-engineered its attack infrastructure so much over the last few months that it is difficult to say for sure.

The effort is likely not just confined to retooling the malware, but also retraining the attackers, Rachwald said. "What we were trying to say is that they are clearly turning around the cyber battleship," he said.

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