Secretary of State John Kerry says he writes emails "with the awareness" that Russian and Chinese hackers are likely reading them, he revealed in an interview with CBS News on Tuesday.
"It is very likely. It is not ... outside the realm of possibility and we know they have attacked a number of American interests over the course of the last few days," Kerry said, referring to recent reports that Russian hackers attacked the Pentagon and Chinese cyberspies were reading US officials' emails.
"It's very possible ... and I certainly write things with that awareness," Kerry added. He did not specify whether he was referring to personal email, government email, or both.
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John Kerry: I write emails assuming that Russia and China are 'very likely' reading them
US-Secretary of State, John Kerry waves after disembarking on May 3, 2015 from his airplane at the Jomo Kenyatta International Airport in the Kenyan capital, Nairobi. Kerry arrived in Kenya for talks on security cooperation and ahead of US President Barack Obama's visit to his late father's home country. The trip to the east African nation is the first high-level visit since 2012, and comes after years of tensions surrounding Kenyan President Uhuru Kenyatta being charged by the International Criminal Court for crimes against humanity. AFP PHOTO/TONY KARUMBA (Photo credit should read TONY KARUMBA/AFP/Getty Images)
US Secretary of State John Kerry (L) speaks with Sri Lankan Tamil National Alliance (TNA) party leader R. Sampanthan (2nd L) in Colombo on May 3, 2015. US Secretary of State John Kerry is in Sri Lanka on a two-day official visit. AFP PHOTO/Ishara S. KODIKARA (Photo credit should read Ishara S.KODIKARA/AFP/Getty Images)
US Secretary of State John Kerry (L) greets Kollupitiye Mahinda Sangharakkhita mahathera at the Kelaniya Rajamaha temple during a visit to Kelaniya on May 2, 2015. US Secretary of State John Kerry arrived on a two-day official visit to Sri Lanka. AFP PHOTO/Ishara S. KODIKARA (Photo credit should read Ishara S.KODIKARA/AFP/Getty Images)
US Secretary of State John Kerry walks off the plane at Kiev Boryspil International Airport in Kiev on February 5, 2015. Kerry flew today in to Kiev where Ukraine's pro-Western leaders hope Washington will send in weapons for their battle against pro-Russian separatists. His visit comes as international pressure grows for an immediate halt to surging violence, with 19 civilians and troops killed in the latest rebel push into government-held territory in eastern Ukraine. AFP PHOTO / POOL / JIM WATSON (Photo credit should read JIM WATSON/AFP/Getty Images)
French president FranÃ§ois Hollande (L) shakes hands with US Secretary of State John Kerry prior to a meeting at the Elysee Palace on January 16, 2015 in Paris. Kerry's visit came after criticism of the US for not sending a top-level representative to a march in Paris on January 11, which drew 1.5 million people and dozens of world leaders in the wake of the attacks. POOL AFP PHOTO RICK WILKING (Photo credit should read RICK WILKING/AFP/Getty Images)
US Secretary of State John Kerry (L) and Pakistan's National Security Advisor Sartaj Aziz smile during a joint press conference at the Foreign Ministry in Islamabad on January 13, 2015. The US and Pakistan pledged on January 13 to work together to wipe out the scourge of terrorism after a massacre at a school in Peshawar, amid reports top diplomat John Kerry will visit the troubled tribal region. AFP PHOTO/ Aamir QURESHI (Photo credit should read AAMIR QURESHI/AFP/Getty Images)
US secretary of State John Kerry poses for a photograph with a girl in Berlin on October 22, 2014. Kerry is on a two-days visit to Germany ahead of the 25th anniversary of the fall of the wall later in the year. AFP PHOTO / POOL/ BRIAN SNYDER (Photo credit should read BRIAN SNYDER/AFP/Getty Images)
JAKARTA, INDONESIA - OCTOBER 20: Australian Prime Minister Tony Abbott (R) and U.S. Secretary of State John Kerry (R) meets for bilateral meeting during their visit for Indonesian President Inauguration Joko Widodo on October 20, 2014 in Jakarta, Indonesia. Kerry is touring Southeast Asian nations to seek support against the (ISIS) Islamic State in Syria and Iraq. (Photo by Oscar Siagian/Getty Images)
US Secretary of State John Kerry boards his plane at Charles de Gaulle Airport on September 16, 2014 in Paris. Kerry was meeting with leaders about strategies to address the threat in the Mideast from ISIS. AFP PHOTO/Brendan SMIALOWSKI/POOL (Photo credit should read BRENDAN SMIALOWSKI/AFP/Getty Images)
Salim al-Juburi (R), Speaker of the Iraqi Parliament shakes hands with US Secretary of State John Kerry before a meeting on September 10, 2014 in Baghdad. Kerry is visiting Iraq where he will meet with leaders, including new Prime Minister Haider al-Abadi, to talk about the threat presented by ISIS and other issues. AFP PHOTO/BRENDAN SMIALOWSKI/POOL (Photo credit should read BRENDAN SMIALOWSKI/AFP/Getty Images)
SYDNEY, AUSTRALIA - AUGUST 11: US Secretary of State John Kerry is pictured during his visit to a replica of Captain Cook's ship 'Endeavour' at the Australian National Maritime Museum on August 11, 2014 in Sydney, Australia. US Sercretary of State John Kerry and US Secretary of Defence, Chuck Hagel will join Australian Foreign Minister Julie Bishop and Australian Defence Minister David Johnston at the annual Australia-Unites States Ministerial Consultations (AUSMIN) in Sydney tomorrow. (Photo by Jason Reed - Pool /Getty Images)
U.S. Secretary of State John Kerry (2nd L) talks on the phone as (From L) Deputy Chief of Staff Jonathan Finer, acting Middle East envoy Frank Lowenstein and Executive Assistant Jennifer Davis look on, at the U.S. ambassador's residence in Paris before his meeting with the Turkish foreign minister on July 26, 2014, within a meeting with the foreign ministers of Qatar and Turkey, primary supporters of Hamas, and top British and French diplomats, to push for a truce in the deadly Israel-Hamas conflict in the Palestinian Gaza Strip. AFP PHOTO / POOL / CHARLES DHARAPAK (Photo credit should read CHARLES DHARAPAK/AFP/Getty Images)
US Secretary of State John Kerry steps off his plane upon his arrival in Paris, France on July 26, 2014. Kerry will continue meetings regarding a cease-fire between Israel and Hamas in Gaza. AFP PHOTO / POOL (Photo credit should read -/AFP/Getty Images)
US Secretary of State John Kerry (L) and US Secreary of the Treasury Jacob Lew (R) visit The Great Wall of China at Badaling, in north of Beijing on July 8, 2014. US officials including Secretary of State John Kerry arrived in Beijing on July 8 for annual strategic and economic talks, with ties strained by differences over hacking and maritime tensions AFP PHOTO / WANG ZHAO (Photo credit should read WANG ZHAO/AFP/Getty Images)
Kurdistan regional government president Massud Barzani (R) greets US Secretary of State John Kerry at the presidential palace in Arbil, the capital of northern Iraq's Kurdistan autonomous region, on June 24, 2014. Kerry arrived in Arbil in a US diplomatic drive aimed at preventing the country from splitting apart in the face of Sunni militants pushing towards Baghdad. AFP PHOTO/POOL/BRENDAN SMIALOWSKI (Photo credit should read BRENDAN SMIALOWSKI/AFP/Getty Images)
US Secretary of State John Kerry waves to hospital staff after visiting the Fistula Clinic at St. Joseph's Hospital, funded by USAID, in Kinshasa, Democratic Republic of Congo, May 4, 2014. Kerry is on his first major tour of Africa, which is focusing on some of the continent's most brutal conflicts. AFP PHOTO / POOL / Saul LOEB (Photo credit should read SAUL LOEB/AFP/Getty Images)
BERLIN, GERMANY - OCTOBER 22: U.S. Secretary of State John Kerry (L) and German Chancellor Angela Merkel give statements to the media prior to talks at the Chancellery on October 22, 2014 in Berlin, Germany. The two leaders discussed the current situation in eastern Ukraine as well as the ongoing conflict against the Islamic State (ISIS), among other issues. (Photo by Pool/Getty Images)
US Secretary of State John Kerry speaks during a visit to the typhoon-ravaged city of Tacloban in the central Philippines on December 18, 2013. Kerry visited the central Philippine city, expressing shock at the death and destruction and vowing that Washington will not abandon its key ally. AFP PHOTO / Jay DIRECTO (Photo credit should read JAY DIRECTO/AFP/Getty Images)
U.S. Secretary of State John Kerry adjusts his earphone during a joint press conference with Brazilian Foreign Minister Antonio Patriota (not framed) at Itamary Palace in Brasilia on August 13, 2013 in the framework of hiss one-day official visit to Brazil. AFP PHOTO/Evaristo Sa/POOL (Photo credit should read EVARISTO SA/AFP/Getty Images)
US Secretary of State John Kerry attends a military ceremony at the anti-narcotics air base in Bogota on August 12, 2013 during his one-day official visit to Colombia. AFP PHOTO/Luis Acosta (Photo credit should read LUIS ACOSTA/AFP/Getty Images)
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Chinese cyberspies have reportedly been reading the private emails of Obama-administration officials and "top national security and trade officials" since 2010.
The report comes amid the ongoing issue of Hillary Clinton's use of a private email server for work-related correspondences while she served as Secretary of State from 2009 to 2013.
Her private server was handed over to the FBI yesterday as part of an ongoing investigation.
Personal inboxes are not the only things being targeted: Chinese hackers — known as the "bullies of cyberspace" — have breached airlines, health-insurance companies, and other government agencies to collect intelligence on US officials and their foreign contacts.
More than 21 million people had their sensitive background and security-clearance information stolen when Chinese hackers breached Office of Personnel Management (OPM) databases in early 2014. The same hackers reportedly attacked United Airlines — the main airline flying in and out of Washington, DC's Dulles Airport — and American airlines.
Kerry emphasized that he is well aware of the changing nature of espionage. He also noted that cyberattacks are of "enormous concern" to the administration.
"Spying has taken place for centuries and the latest means of spying is to be going after peoples' cyber," he said. "Companies spend billions of dollars to protect themselves, the United States government does the same."
Still, as geopolitical expert Ian Bremmer noted to Business Insider in June, "there's no effective defense against these attacks and, as we've seen, there's also no effective deterrence."