Yesterday, we filed a Freedom of Information Act request with the FBI asking for details about a surveillance tool we know too little about, called a port reader. According to news reports , port readers copy entire emails and instant messages as they move through networks, in real time. They then delete the contents of the messages, leaving only the "metadata" — the sender, recipient, and time of a message, and maybe even the location from which it was sent — behind for the government. According to the same reports, the FBI is taking steps to install port readers on the networks of major U.S. phone and Internet companies, going so far as to make threats of contempt of court to providers that don't cooperate.

In our request, we asked the FBI to tell us more about port readers. What metadata exactly are they collecting? Has the FBI succeeded in getting any internet or phone providers to install them? If so, how much data has been collected so far? And is the FBI able to ensure that the content port readers incidentally collect is never retained long enough for the government to use it? You can read our full request and see all of our questions here .

We want to know more about port readers because we are concerned about the threat they pose to Americans' privacy. Existing reports tell us that port readers collect 13 separate fields of metadata, and right now we don't know what all of them are. This is a problem because metadata can be extremely sensitive. Losing privacy for the metadata of even a single message can be damaging, if that message is between a journalist and her confidential source, for instance, or a patient and his therapist.

Reports seem to conflict on the question of whether port readers are intended to collect small amounts of targeted data or large amounts of data in bulk. If they're meant for bulk collection, the information gained would be all the more revealing. Large volumes of metadata allow for deductions about people's relationships, friendships, and professional lives. As Judge Leon, who sits on the District Court in Washington, D.C., recently explained , metadata can "reveal an entire mosaic — a vibrant and constantly updating picture of the person's life." For an illustrative example of this, you can read this blog by my colleague Kade Crockford at the ACLU of Massachusetts, and watch the embedded presentation by students at MIT.

Thanks to Edward Snowden, we all know that our government has myriad ways of tracking our activities and communications online. But we shouldn't have to sacrifice our privacy rights to participate in modern life. We hope this request results in greater transparency about a surveillance tool the public currently knows too little about, and that port readers are being used in a way that protects the privacy of innocent Americans.