I have had this question rolling around in my head for several months now. I attended a presentation by a police officer who specialized in computer security. One of his main jobs is to scan computers for child pornography. He said he did this by inserting a flash drive given to the police department by a federal agency (I believe it was the NSA) and looking at what the flash drive came up with. I raised my hand and asked him what he did if the computer's owner had encrypted files and he said that it didn't matter. He specifically referenced TrueCrypt when he said, " Some people use encryption programs such as TrueCrypt to try to hide their files, but all it does is make the flash drive run a little longer."
So how can this work? I am not looking to start an argument about the overreaching powers of the federal government. I am just curious as to how this little flash drive can detect hidden TrueCrypt volumes and then see if there is illegal pornography on them.