As Hillary Clinton remains under fire after revelations that material deemed classified was sent through an unsecure home server she used as secretary of state for email, a review of records makes clear that the leakage of secrets is a State Department problem dating to the George W Bush administration, if not earlier.
The matter has become an issue in Clinton's front-running campaign for the Democratic presidential nomination. And the trend may have accelerated under Clinton as email use became more frequent.
One example: during the deadly 2012 attack on US facilities in Benghazi, Libya, State Department officials in Washington were emailing one another with updates in real time. Embedded in those messages were nuggets of classified information, including an apparent reference to a CIA facility that was a closely guarded secret.
When the emails were released last year, that and other information found to be classified were censored from public view.
Clinton's use of a home server makes her case unique, but it's not clear whether the security breach would have been any less had she used government email. The State Department only systematically checks email for sensitive or classified material in response to a public records request.
Clinton insists she didn't send or receive information marked classified, and there is no evidence she did. But information can be classified without being marked. Government investigators have found material they believe was classified when sent in several dozen of 30,000 emails that the former secretary of state has turned over.
In five messages that date to Condoleezza Rice's tenure as secretary of state during the George W Bush administration, large chunks are censored on the grounds that they contain classified national security or foreign government information.
In a December 2006 email, for example, diplomat John J Hillmeyer appears to have pasted the text of a confidential cable from Beijing about China's dealings with Iran and other sensitive matters. Large portions of the email were marked classified and censored before release.
Now released, the emails have been posted on the State Department's searchable reading room.
On the night of the Benghazi attack on September 11, 2012, department officials emailed one another about extraordinarily sensitive matters, including the movement of Libyan militias and the locations of key Americans.
