Sen. Ron Wyden provided the details in a statement after the Internal Revenue Service and Treasury Department briefed the Senate Finance Committee on the matter.
Wyden said that while the hack “appears to be significant,” there is no indication those responsible compromised taxpayer data.
He added that department officials do not know the full extent of the hackers’ actions or exactly what information they stole.
Treasury Secretary Steven Mnuchin told the cable news network CNBC on Monday “there has been no damage, nor have we seen any large amounts of information displaced.”
Microsoft has said the hackers compromised dozens of Treasury Department email accounts, and that it had identified more than 40 government agencies, tech companies and nongovernmental organizations whose systems had been infiltrated.
Cybersecurity experts have said the breach began early this year when the hackers inserted malware into a software update for a product that many companies use to monitor their networks. The malware gave the hackers remote access to the affected networks.
Secretary of State Mike Pompeo and Attorney General William Barr have said Russia appears to be responsible. Russia denies being involved.
