The probe into the hack of Tarkos, a Russian tech firm that’s been blamed for an attack on the DNC and Hillary Clinton’s campaign, will not be resolved, Microsoft CEO Satya Nadella told analysts in a presentation at the company’s Build conference today.

Nadella said that the investigation, which has been going on for several years, has not been able to definitively determine the origin of the hack, which the FBI and CIA are investigating.

The probe will be open for a few more months, he said.

“What we do know is that the source is not necessarily Russia,” he said, adding that there are a lot of indicators of attempts to break into Tarko’s systems that are consistent with attempts to hack a third party.

“The investigation will also examine whether Tarkom’s system was compromised, and if so, how.

Nadell said the firm would work with cybersecurity experts to help determine how Tarkas network was breached.

He also said Microsoft would be providing Tarkum with “technical support” in the coming months.

Microsoft has hired cybersecurity firm CrowdStrike to help analyze the Tarkoman attack.