WASHINGTON (CBSNewYork/AP) — Russia-linked hackers tried at least five times to pry into Hillary Rodham Clinton’s private email account while she was secretary of state, emails released Wednesday show.

It was unclear if she clicked on any attachment and exposed her account.

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Clinton received the infected emails, disguised as speeding tickets, over four hours early on the morning of Aug. 3, 2011. The emails instructed recipients to print the attached tickets, which would have allowed hackers to take control of their computers.

Security researchers who analyzed the malicious software in September 2011 said that infected computers would transmit information from victims to at least three server computers overseas, including one in Russia. That doesn’t necessarily mean Russian intelligence or citizens were responsible.

Clinton has said repeatedly that the unusual homebrew server she used was secure.

But the phishing attempts highlight the risk of Clinton’s unsecure email being pried open by foreign intelligence agencies, even if others also received the virus concealed as a speeding ticket from Chatham, New York in upstate Columbia County. The email misspelled the name of the city, came from a supposed New York City government account and contained a “Ticket.zip” file that would have been a red flag.

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Most commercial antivirus software at the time would have detected the software, identified it as dangerous and prevented users from infecting themselves. It was unclear if the State Department’s network security would have flagged the infected message, or what precautions were in place protecting Clinton’s server in the basement of her home in Chappaqua.

The State Department and other government agencies, during Clinton’s tenure and after, suffered its own series of hacking attacks. U.S. counterterrorism officials have linked them to China and Russia.

Clinton has been dogged for months by questions about her email practices. She initially described her choice as a matter of convenience.

But Clinton has apologized for the way she handled her emails.

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“As I look back at it now, even though it was allowed, I should have used two accounts,” she said earlier this month. “One for personal, one for work-related emails. That was a mistake. I’m sorry about that. I take responsibility.”