Doh, some of these options seem horrible: eg, allowing the data to be extracted automatically using standard tools. If you can automatically detect hidden data,

Doh, some of these options seem horrible: eg, allowing the data to be extracted automatically using standard tools. If you can automatically detect hidden data, it's only hidden from people who aren't looking. If your data is worth hiding, it's worth hiding from people who know how to use "find -exec" (or had someone else set up an automated sweep program for them).