The DLL file disguised as a McAfee antivirus executable was confirmation that something was amiss. That’s what convinced Office of Personnel Management contractor Brendan Saulsbury that this was not legitimate traffic in the agency’s network: OPM doesn’t use McAfee’s AV software.

Saulsbury told a congressional committee earlier this year that he was the first person to spot malicious activity that ultimately revealed the now-infamous and historic data breach at the Office of Personnel Management (OPM), shooting down previous reports that it was found by forensics security vendor CyTech Services during a product demonstration at the agency in April 2015.

A letter late last month from Rep. Elijah Cummings (D-Md.) of the House Oversight Committee to the House Permanent Select Committee on Intelligence said original claims that forensics firm CyTech Services was the first to spot the cyberattack on OPM was “inaccurate” and that OPM, via its Cylance security tool, found the malware five days before CyTech’s systems did. Cummings provided details on pieces of the puzzle that led to the breach discovery.

In an interview with Cummings’ committee on February 17 of this year, Saulsbury said that on April 16, 2015, he spotted malware on two different OPM servers “beaconing” out to a command and control server:  “[W]e were able to determine that the actual malware was a DLL file that was called mcutil.dll. It was basically trying to fly under the radar as if it was a McAfee antivirus executable. The problem is that OPM doesn’t use McAfee, so that stood out right there to us that, at that point, I was 100 percent certain that this is malware that is beaconing out.”

The account relayed in Cummings’ letter to the Intelligence Committee raises questions over how another contractor, CyTech Services, could have been led to believe it found the malware at OPM a few days later.

OPM did not offer a direct comment on the letter documenting the new information, but instead referred to the agency’s comments mentioned in Rep. Cummings’ letter. According to Cummings, Jeff Wagner, director of security operations for OPM, told the committee it was Cylance’s security tool that spotted the malware: "Mr. Wagner also explained that the tool used to identify the malware was developed by a different contractor, Cylance, that Ms. Seymour [former OPM CIO] had hired previously to enhance OPM's cybersecurity: Because of the unique capability of Cylance in mapping binary files as opposed to looking at direct signatures, we knew it was going to be able to immediately find any malware no matter what the indicators were.”

Wagner in an April 17, 2015 email to Seymour said Cylance representatives would be arriving at OPM to assist with forensics since it was "their tool that found the Malware." Cummings also said the email was sent five days before CyTech found the malware in OPM systems.

Ben Cotton, president and CEO of CyTech, told Dark Reading this week that he didn’t claim to be the first to discover the malware on OPM’s systems. “I don’t know what happened prior to us arriving on April 21,” he says. “On April 21, we ran [our forensics product] as a demo, and we discovered that malware on three live processes inside OPM’s operational network.”

He says he and his team showed this to the OPM team in the room at the time, and then CyTech became involved in an incident response operation. “Our software found it 12 minutes after” loading, he says. “It was still live in their operational network, exploiting servers and systems we found it on.”

OPM did not appear to be in an incident response posture at the time, he says, and his company assisted with IR afterward, until around May 1, also supporting the FBI and US Secret Service, he says. Cotton says the OPM team never mentioned to him or his team prior to the demo that the malware had been discovered previously on OPM systems.

Meanwhile, Cotton says he’s awaiting payment for the IR services his team offered OPM.

Some 21.5 million individuals had their social security numbers, residency and employment history, family, health, and financial history exposed in the massive data breach of OPM's background-check investigation database.

Of the 19.7 million individuals who had applied for the background checks, 1.1 million had their fingerprint scans exposed as well. The remaining 1.8 million people affected by the breach were spouses or other members of the applicants' households.

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