Powell's antiquated AOL account, which worked over a phone line in his office at the State Department, might have been more vulnerable to attack by hackers than the private email server the Clinton used during her tenure as secretary.
Powell said in a statement he viewed his use of private email to communicate with foreign leaders and senior U.S. officials as private conversations similar to phone calls. He said he was unaware of any requirement that those messages be preserved as government records, potentially subject to public release.
"I have been interviewed by the State Department (Inspector General) and the FBI about my actions and decisions," Powell said Thursday. "I stand by my decisions and I am fully accountable."
A retired Army general, Powell served as America's top diplomat during Republican President George W. Bush's first term. His exchange with Clinton was released Wednesday by congressional Democrats.
Powell wrote to Clinton in January 2009 that he had "a personal computer that was hooked up to a private phone line" so he could communicate with friends and foreign leaders directly "without it going through the State Department servers."
Powell also warned Clinton in 2009 "there is a real danger" if it were to became known she was using a smartphone to send emails because they could become official government records subject to release under the Freedom of Information Act.
Republicans have sought to portray the Democratic presidential nominee's use of a private server to conduct official business as reckless, saying her homebrew email setup was probably targeted by foreign intelligence agencies.
A yearlong investigation by the FBI focused on whether Clinton sent or received classified information using the private server, which was not authorized for such messages. FBI Director James Comey said in July that his agents didn't find evidence to support any criminal charges or direct evidence that Clinton's private server was hacked. He suggested that hackers working for a foreign government may have been so sophisticated they wouldn't have left behind any evidence of a break-in.
In Powell's case, however, it is known that his private email account was eventually breached.
In 2012 and 2013, a Romanian hacker known as Guccifer targeted Powell's AOL account, as well as the accounts of former President George W. Bush's sister and dozens of others.
The hacker then leaked emails Powell exchanged with a female Romanian diplomat with whom he carried on years of personal correspondence after meeting while he was secretary of state. Powell, who is married, denied having an affair with the woman.
The hacker also accessed Powell's Facebook account, sending out posts under the former secretary of state's name stating "You will burn in hell, Bush!" and "Kill the illuminati!"
In addition to Powell, Guccifer hacked the email account of Sidney Blumenthal, a Clinton confidant. The subsequent leak of Blumenthal's emails was the first time outsiders became aware of Clinton's private "clintonemail.com" address, which she used to communicate with Blumenthal.
Guccifer, whose real name is Marcel Lazar, was subsequently arrested and extradited to the United States. He was sentenced last week to more than four years in federal prison.
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