Putin’s spies have “almost certainly” infiltrated the FBI and CIA, both agencies have clamed.
Experts in the agencies fear detailed information carries more value and is more critical now than ever as Russia's war with Ukraine continues.
Former spooks have made the claims in a book about Robert Hanssen, a US spy who is serving 15 life sentences in jail.
The prisoner worked as a spy for the US and Russia from 1979 until his 2001 arrest, and sold many secrets to Russia including details of the US's defence strategy,
His double-handed exploits are highlighted by Lis Wiehl, an ex- federal prosecutor, in the book titled: “A Spy In Plain Sight.”
Ms Weihl told The Sun everyone she spoke to while compiling the book suggested there were probably multiple Hanssens doing the same in America today.
She said: “We have to be very aware that this could happen again.
“It was shocking to me when I did my interviews and asked the FBI agents and CIA officers.
“Every interview I ended with, ‘Could there be another Hanssen today?’ and, to a person, a hundred percent, the response was yes.
“And the follow up with many of them was that there probably already is.”
A former FBI Special Agent, Jack Thompson, is interviewed in the book and was told he had “no reason to believe there isn’t a recruitment in place right now in the FBI, the CIA, and the DOE.”
He added: “I can say almost with certainty that people in the DOE have been recruited by foreign intelligence services.”
Ms Weihl reckoned that as a former KGB agent, Putin would know athe benefits of having an ear in American affairs.
She said: "We can't be lackadaisical, we have to keep putting pressure on the institutions that are supposed to protect us like the FBI and the CIA to monitor their own.
"The information they have at the top level is absolutely critical to the wellbeing of all of us."
The Mirror told this month how Vladimir Putin is under pressure as Russian spies are reportedly turning on the Kremlin boss blaming him for the failures of the " special military operation ".
Russian spooks are said to be at odds with Putin over the handling of their invasion, an expert on the Russian secret service has said.
As a result, Putin is said to have launched a purge of his intelligence services, including the spies from the Fifth Service group of the Federal Security Bureau - the department who were working on Ukraine.
This group is believed to have been working in Ukraine for years to try and destabilise the country ahead of the invasion.
