NEWS YOU CAN USE? Why printers add secret tracking dots.

These “microdots” are well known to security researchers and civil liberties campaigners. Many colour printers add them to documents without people ever knowing they’re there.

In this case, the FBI has not said publicly that these microdots were used to help identify their suspect, and the bureau declined to comment for this article. The US Department of Justice, which published news of the charges against [Reality] Winner, also declined to provide further clarification.

In a statement, The Intercept said, “Winner faces allegations that have not been proven. The same is true of the FBI’s claims about how it came to arrest Winner.”

But the presence of microdots on what is now a high-profile document (against the NSA’s wishes) has sparked great interest.

The EFF has an online guide to help you “read” printer microdots.