Much has been made of the fact that Hillary Clinton's personal computer contained classified email. This sounds bad to anyone who is unaccustomed to dealing with classified information, but not so much to those of us with security clearances (full disclosure: I've had one since I was a Ph.D. student the 1970s). We receive annual training and are constantly reminded that there can be classified -- even top secret -- information in the public domain. Like messages Clinton received, this publicly-available information is not marked as classified.
It's obvious that Clinton's harshest critics have never passed Classified Training 101. As is the case with many of their other attacks on the Democratic candidate, their statements reveal an utter lack of basic subject matter knowledge. For example, Donald Trump mocked Clinton on the matter in a tweet, saying "Lyin' Hillary Clinton told the FBI that she did not know the 'C' marking on documents stood for classified. How can this be happening?" But (C) does not stand for classified in government documents. It stands for confidential. That means it has already been determined by classification experts not to be secret (let alone top secret).
So how did top secret information get onto Secretary Clinton's private computer? According to reports, it was emailed to her. It is instructive to discuss my own experience to understand why the owner of a computer with classified information on it has not necessarily done anything wrong.
In the summer of 2003, I used my own personal computer to read a about the controversy associated with Iraq's alleged efforts to develop weapons of mass destruction, which was the justification for the US invasion that year. Some of the stories I downloaded to read were about the supposed purchase by Iraq of yellowcake extracted from uranium ore. On my reading list was the Washington Post opinion piece, "Mission to Niger" by Robert Novak in which he revealed the then-classified identity of Valerie Plame as a covert CIA operative. This information was not marked by Novak as classified and was passed around the internet, emailed, and downloaded onto private servers everywhere, including those belonging to people like me, with top secret security clearances.
This example is easy to talk about now because the information has since been declassified. If this happened once, it has probably happened many times. I and most other Americans remain unaware of what unmarked classified information may also be lurking on our private computer drives.
As an ordinary low-level national security worker bee, most of the work-related email I get is related to my unclassified projects. Unfortunately there have been a couple of occasions in which an unmarked classified message was accidentally sent to me. In one case, the sender received a security infraction. Nobody ever suggested that I did anything wrong. I was just the passive recipient and I did not even read them. That's the way it works.
Holders of security clearances are required to receive random drug tests as well as polygraph examinations in which we are asked if we have ever mishandled classified information. I've never failed such a test, despite having downloaded a file to my private computer that contained the classified identity of a covert CIA agent. The vast majority of national security colleagues I've spoken with cannot say with certainty that they have never had classified information on their private computers. They reject the notion that classified email in Secretary Clinton's inbox is evidence that she did something wrong because they understand that if they were hacked they would probably be in the same boat.
On the other hand, there are those who think that the emails are evidence that Clinton knowingly mishandled classified information, and for that reason is unfit to be President. I have heard from some of these people. Without exception they disagree with the candidate on other issues, such as abortion rights, gun safety, and climate change. And I've never heard them criticize Robert Novak, Karl Rove, Dick Cheney, or Scooter Libby. Their opinions on the matter are obviously influenced by their politics.
There is reason to be skeptical of claims that Clinton did something wrong by having received classified messages on her computer. We've all probably had that happen to us. So what? It's not evidence of a crime. By itself, it's not even evidence of an infraction.