WASHINGTON (AP) — Dozens of email accounts at the Treasury Department were compromised in the massive breach of U.S. government agencies being blamed on Russia.

That's according to an Oregon Democrat, Sen. Ron Wyden, who says hackers broke into systems used by the department’s highest-ranking officials.

Wyden issued a statement Monday after he and other members of the Senate Finance Committee were briefed by the IRS and the Treasury Department.

Wyden says that though there is no indication that taxpayer data was compromised, the hack “appears to be significant." In addition, the breach appears to involve the theft of encryption keys from U.S. government servers, Wyden said.

“Treasury still does not know all of the actions taken by hackers, or precisely what information was stolen,” Wyden said in a statement.

It is also not clear what Russian hackers intend to do with any emails they may have accessed.

A Treasury Department spokeswoman declined to comment on Wyden’s statement.

Treasury was among the earliest known agencies reported to have been affected in a breach that now encompasses a broad spectrum of departments. The effects and consequences of the hack are still being assessed, though the Department of Homeland Security’s cybersecurity arm said in a statement last week that the intrusion posed a “grave” risk to government and private networks.

In the Treasury Department’s case, Wyden said, the breach began in July. But experts believe the overall hacking operation began months earlier when malicious code was slipped into updates to popular software that monitors computer networks of businesses and governments.