The email accounts of the highest-ranking Treasury Department officials were compromised in a massive breach of U.S. government systems, according to Sen. Ron Wyden (D-Ore.). Wyden made the remarks on Monday after being a briefing on the hack to the Senate Finance Committee by the Internal Revenue Service and the Treasury Department. Wyden said the hack “appears to be significant” and appears to have involved the theft of encryption keys. “Treasury still does not know all of the actions taken by hackers, or precisely what information was stolen,” Wyden said in a statement. A Treasury Department spokeswoman declined to comment on Wyden’s statement. Secretary Steven Mnuchin said in a CNBC interview on Monday that the hack impacted the Treasury’s unclassified systems, but the department has not seen any damage. “We do not see any breaking into our classified systems. Our unclassified systems did have some access,” Mnuchin said about the massive hack. “I will …