Roger Stone
© Joe Raedle / Getty ImagesRoger Stone, a longtime political adviser and friend to President Donald Trump, speaks before signing copies of his book ‘The Making of the President 2016’ at the Boca Raton Marriott on March 21, 2017
The question of whether political operative Roger Stone helped Russian hackers break into the email of Democratic politicians, to some people, invites another: Who says the hackers were Russian?

The FBI does, and so do several U.S. intelligence agencies, as they've declared repeatedly over the past five months. But among private-sector computer security companies, not everybody thinks the case is proven.

"I have no problem blaming Russia for what they do, which is a lot," said Jeffrey Carr of the international cybersecurity company Taia Global Inc. "I just don't want to blame them for things we don't know that they did. It may turn out that they're guilty, but we are very short on evidence here."

As Carr notes, the FBI never examined the servers that were hacked at the Democratic National Committee. Instead, the DNC used the private computer security company CrowdStrike to detect and repair the penetrations.

"All the forensic work on those servers was done by CrowdStrike, and everyone else is relying on information they provided," said Carr. "And CrowdStrike was the one to declare this the work of the Russians."

The CrowdStrike argument relies heavily on the fact that remnants of a piece of malware known as AGENT-X were found in the DNC computers. AGENT-X collects and transmits hacked files to rogue computers.

"AGENT-X has been around for ages and ages, and its use has always been attributed to the Russian government, a theory that's known in the industry as 'exclusive use,'" Carr said. "The problem with exclusive use is that it's completely false. Unlike a bomb or an artillery shell, malware doesn't detonate on impact and destroy itself.

"You can recover it, reverse-engineer it, and reuse it. The U.S. government learned a lesson about that when it created the Stuxnet computer worm to destroy Iran's nuclear program. Stuxnet survived and now other people have it."

Carr said he is aware of at least two working copies of AGENT-X outside Russian hands. One is in the possession of a group of Ukrainian hackers he has spoken with, and the other is with an American cybersecurity company. "And if an American security company has it, you can be certain other people do, too," he said.

There's growing doubt in the computer security industry about CrowdStrike's theories about AGENT-X and Russian hackers, Carr said, including some critical responses to a CrowdStrike report on Russian use of the malware to disable Ukrainian artillery.

"This is a close-knit community and criticizing a member to the outside world is kind of like talking out of turn," Carr said. "I've been repeatedly criticized for speaking out in public about whether the hacking was really done by the Russians. But this has to be made public, has to be addressed, and has to be acknowledged by the House and Senate Intelligence Committees."