Specific comment: Sergey Goldgaber suggests hiding files amongst the disk blocks marked "deleted" by the filesystem. This sounds practically equivalent to implementing an alternative file system with its own FAT, etc. In addition to the problems and solutions Sergey mentioned, the true/surface/original filesystem must be slightly modified so that it doesn't bash the hidden filesystem in the process of making new files. Of course, it will look rather funny when the disk runs out of space several tens of megabytes below the manufacturer's specs. This hidden file system feature might fit in naturally with SecureDrive which implements an encrypted file system. General comments: Encryption and mimicry are both a matter of economics. Unfortuneately, as with most mimicry, the effort needed to find the hidden filesystem is easier than the effort needed to implement and maintain the hidden filesystem. ("Effort" here is primarily programmer and user effort, not computer resources). It also costs to hide encrypted data in noise; in this case the cost is mostly bandwidth. This must be traded off with the fact that nobody is going to be either (a) banning compression or noise-containing data or (b) sampling significant fractions of compressed and noisy files that cross the net to see if they're actually encrypted. Both passage and enforcement of anti-cryptography laws will be greatly discouraged by widespread use of mimicry (including steganography). This is also a good opportunity to put in my plug _in favor_ of "security through obscurity" as a good practical solution to some problems. For example, the task of scanning the net gets super-linearly more expensive with the number of data formats used (since the cost of implementing software is super-linear with its raw complexity). Simply having a wide variety of fax, compression, sound, video, encryption, etc. formats will quickly make the cost of automated scanning efforts prohibitive. Interoperability favors standardization, but security and privacy favor incompatability with the popular formats used by the snoopers. Nick Szabo szabo@netcom.com