Sen. Mitt Romney, a Utah Republican, slammed the White House for "inexcusable silence and inaction" for almost a week following reports of Russian cyberattacks on software company SolarWinds and, by extension, government agencies. 

FEDERAL AUTHORITIES SOUND ALARM OVER SUSPECTED RUSSIAN HACK AGAINST US

The U.S. Cybersecurity and Infrastructure Security Agency announced the intrusion involving SolarWinds Orion products, which is now under FBI investigation, on Sunday and directed all federal agencies to disconnect from the breached network-management software.

President Trump was reportedly briefed on the suspected Russian hack on Thursday but has yet to comment publicly on what Romney said would be the digital equivalent of discovering "Russian bombers have been repeatedly flying undetected over our entire country."

Top senators on the Armed Services Committee have cautioned that the cyberattack on U.S. government is "ongoing" and "has the hallmarks of a Russian intelligence operation."

The hack compromised federal agencies and "critical infrastructure" in a sophisticated attack that was hard to detect and will be difficult to undo, the cybersecurity agency said in an unusual warning message Thursday. The Department of Energy acknowledged it was among the agencies that had been hacked.

WHITE HOUSE CONFIRMS CYBERATTACK REPORT ON U.S. TREASURY BY FOREIGN GOVERNMENT

The attack, if authorities can prove it was carried out by Russia as experts believe, creates a fresh foreign policy problem for Trump in his final days in office.

Trump's silence on the matter has garnered scrutiny from both sides of the aisle, especially when paired with his past handling of issues concerning Russia, including eliminating a White House cybersecurity adviser and downplaying Russian interference in the 2016 presidential election. 

Romney said the attack illustrates an "alarming U.S. vulnerability," and an "apparent cyber warfare weakness." 

"It's past time for a national security re-set that prioritizes cybersecurity capabilities and defenses," he said. 

Thomas Bossert, a former Trump Homeland Security adviser, said in an opinion article in The New York Times earlier this week that the U.S. should now act as if the Russian government had gained control of the networks it has penetrated.

"The actual and perceived control of so many important networks could easily be used to undermine public and consumer trust in data, written communications and services," he wrote.

RUSSIA'S SUSPECTED HACKING OPERATION TARGETED 5 US AGENCIES, 18K ENTITIES

Meanwhile, Trump's lack of response stands in stark contrast to the posture of incoming President Joe Biden, who promised to "make dealing with this breach a top priority from the moment we take office."

"We need to disrupt and deter our adversaries from undertaking significant cyberattacks in the first place," he said. "We will do that by, among other things, imposing substantial costs on those responsible for such malicious attacks, including in coordination with our allies and partners."

"There’s a lot we don’t yet know, but what we do know is a matter of great concern," Biden said following the attack. 

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The Associated Press contributed to this report.