Authorities believe that the massive “SolarWinds” hack allegedly carried out by Russia last year successfully breached the email accounts of then-DHS acting secretary Chad Wolf and dozens of other officials at the Department of Homeland Security, three sources familiar with the matter told ABC News.

In fact, the email accounts of top officials at Cybersecurity and Infrastructure Security Agency — the very DHS agency charged with fighting cyber threats — may have been compromised by the cyberattack, according to one former government official familiar with the matter.

In a statement, DHS acknowledges a “small number” of employees accounts were targeted in the breach, but there are no indicators that their networks are compromised as of now.

“A widespread intrusion campaign targeted many federal government and private sector entities, including DHS,” according to a DHS spokesperson.

“Upon learning about the campaign, the Department took immediate steps to respond to the incident, including leveraging response teams from CISA and private sector partners, to continue executing its mission,” the spokesperson said. “However, this widespread intrusion campaign has again shown that our strategic adversaries are sophisticated, persistent, and have increasing capabilities.”

The massive hack, discovered in December, affected nine federal agencies, according to Deputy National Security Adviser for cyber Anne Neuberger.

Those responsible were “likely of Russian origin,” that the hack was “launched from inside the United States” and that it could take “several months” to complete the investigation, she said at a press briefing in February.

The administration has yet to outline what exactly their response will be to the hack.

FBI Director Chris Wray, asked earlier this month by Senate Judiciary Chairman Sen. Dick Durbin, D-Ill., what the U.S. government’s response should be to the SolarWinds hack, said he didn’t want to answer specifically because “discussing the response in any detail is probably something that would be better done in a classified setting. That by itself might give you a little bit of a hint.”

Wray said more generally that coming back from the SolarWinds hack would be a “long, hard slog,” even using the strategy that has been most effective for the U.S. in the past regarding countering cyber adversaries.

ABC News’ Alexander Mallin contributed to this report.