Not that we need another one but this 2007 Scientific American article has a frightening illustration of the Iron Law of Data Collection at work. Here in the U.S. the Constitution provides for a decennial census of the population in order to apportion members of the House of Representatives and direct taxes among the states. Over the years it's evolved from a simple head count into a nosy inquiry into such things as how many bathrooms each household has. Many people object to the snooping but there's been no organized resistance to it.
Despite years of pledges about confidentiality and specific denials about its use to round up Japanese-Americans during WWII, it turns out that that's exactly what happened. They had to change the law to allow the Census Bureau to release the information and for years the Census Bureau has insisted that they released only neighborhood information on Japanese-Americans but not the “microdata” about them. If you're familiar with the Iron Law, you won't be surprised to learn that that was a lie. Read the Scientific American article for the details.
You can understand why the Census Bureau would resist admitting this (other than an institutional sense of shame): if people felt that their personal information would be released whenever the government felt they had a good reason, they would be less forthcoming with that information. Then how would the government know how many bathrooms we had?