The review was conducted by Echelon, a company with close ties to the Russian military, on behalf of Russia's Federal Service for Technical and Export Control (FSTEC), a defense agency tasked with countering cyber espionage.
Echelon president and majority owner Alexey Markov said in an email to Reuters that he is required to report any vulnerabilities his team discovers to the Russian government.
But he said he does so only after alerting the software developer of the problem and getting its permission to disclose the vulnerability. Echelon did not provide details about HPE's source code review, citing a non-disclosure agreement with the company.
FSTEC confirmed Markov's account, saying in a statement that Russian testing laboratories immediately inform foreign developers if they discover vulnerabilities, before submitting a report to a government "database of information security threats."
One reason Russia requests the reviews before allowing sales to government agencies and state-run companies is to ensure that U.S. intelligence services have not placed spy tools in the software.
HPE said no "backdoor vulnerabilities" were discovered in the Russian review. It declined to provide further details.
HPE said it allows Russian government-accredited testing companies to review source code in order to win the Russian defense certifications it needs to sell products to Russia's public sector.
An HPE spokeswoman said source code reviews are conducted by the Russian testing company at an HPE research and development center outside of Russia, where the software maker closely supervises the process. No code is allowed to leave the premises, and HPE has allowed such reviews in Russia for years, she said.
Those measures ensure "our source code and products are in no way compromised," she said.
Some security experts say that studying the source code of a product would make it far easier for a reviewer to spot vulnerabilities in the code, even if they did not leave the site with a copy of the code.
In a 2014 research paper, Echelon directors said the company discovered vulnerabilities in 50 percent of the foreign and Russian software it reviewed.
Still, security analysts said the source code review alone, even if it yielded information about vulnerabilities, would not give hackers easy entry into the military systems. To infiltrate military networks, hackers would need to first overcome a number of other security measures, such as firewalls, said Alan Paller, founder of the SANS Institute, which trains cybersecurity analysts
Paller also said HPE's decision to allow the review was not surprising. If tech companies like HPE want to do business in Russia, "they don't really have any choice," he said.
HPE declined to disclose the size of its business in Russia, but Russian government tender records show ArcSight is now used by a number of state firms and companies close to the Kremlin, including VTB Bank and the Rossiya Segodnya media group.
Whether the customer is Russia or the United States, overlooked errors in software code can allow foreign governments and hackers to penetrate a user's computer.
Exploiting vulnerabilities found in ArcSight's source code could render it incapable of detecting that the military's network was under attack, said Allen Pomeroy, a former ArcSight employee who helped customers build their cyber defense systems.
"A response to the attack would then be frankly impossible," Pomeroy said.
The HPE spokeswoman said Reuters' questions about the potential vulnerabilities were "hypothetical and speculative in nature."
HPE declined to say whether it told the Pentagon of the Russian review, but said the company "always ensures our clients are kept informed of any developments that may affect them."
A spokeswoman for the Pentagon's Defense Information Systems Agency, which maintains the military's networks, said HPE did not disclose the review to the U.S. agency. Military contracts do not specifically require vendors to divulge whether foreign nations have reviewed source code, the spokeswoman said.
The U.S. military agency itself did not require a source code review before purchasing ArcSight and generally does not place such requirements on tech companies for off-the-shelf software like ArcSight, the Pentagon spokeswoman said. Instead, DISA evaluates the security standards used by the vendors, she said.