Ex post facto is a legal term that basically means "after the fact." If you perform a certain act today and tomorrow this act becomes illegal, you can't be arrested for breaking the law because it wasn't illegal when you did it.
I have brought up this term because, in a way, it intersects with the massive surveillance apparatus of the US government.
We are being told that no one is listening into our phone conversations or reading our emails in real time. While I distrust a good deal of what government officials say -- particularly when it comes to the NSA, CIA and FBI -- I actually believe that this assertion is true. I don't think it's true simply because the government says it is -- it has far more to do with the volume of information being scooped up. With billions of data sets being collected each month, there simply aren't enough government employees and private contractors to do the job.
So, if no one is listening into our phone calls or reading our online communications in real time, then maybe we don't have a cause for concern? I wouldn't say that at all and this is where ex post facto comes into play.
If at a later date, either the government or one of their many private contractors decides that you or I is a target -- this could be for many reasons other than suspected illegal activities -- they now have the ability to look into our communications "after the fact." They can dig around until they find something embarrassing and then utilize this information either to bring charges against us or to pressure us to do or not do something. It's what we could call a quasi legal or patently illegal form of blackmail!
Let's say you feel that you were injured by a certain product and so you decide to bring a lawsuit against the corporation that manufactures it. If this corporation happens to be one of those that has a hand in the NSA spying, they might decide to dig through your past communications to find something embarrassing as a way to try to intimidate you into dropping the suit.
Let's say you are a volunteer with an organization that opposes a particular law, regulation or policy. Your group is planning a big demonstration and march to voice your concerns. The government knows that you are one of the chief organizers and so they are determined to remove you from the picture. So, they cull through your records to find something they can charge you with or, as above, something embarrassing that they will threaten to expose unless you bow out.
The loss of privacy paints a bright red target on everyone's head. Since almost every person who has ever lived has a few skeletons in their closet, those skeletons become potential pressure points in the hands of the unscrupulous. Most of us can be convinced to do or say anything in order to keep our dirty laundry out of public view!