Kindle codes in converted epubs

[Hoods7070]

My question: someone pointed out to me that there is a code in Kindle books: avk:bin followed a long string of numbers - purportedly showing all your details, and I guess sending info back and forth from your Kindle to Amazon. Obviously those of us with epub readers remove D*R*M then convert to epub in Calibre (or however). Is this coding automatically removed by a conversion to epub in Calibre, or has it already been removed as part of the D*R*M removal, whatever process you have used to remove it?

I can locate this code in an original unconverted AZW3 by renaming the extension to .txt and searching the (binary?) result in notepad. It's obfuscated, but the essentials are easily visible. (I am talking about an azw3 from which I have removed the D*R*M.) However, once I have converted it to an epub, there's no sign of any such thing. Also, CAN hidden stuff be truly *hidden* in epub files, which are, per my theories, just txt and html?

This is idle curiosity as I have never owned a Kindle (and never will) but have had a string of epub readers. Initially, and necessarily, I bought 80% of my books from Amazon. It was the only seller available to Australian for a long time, plus a few others that came and went and which were more of a hassle. Now several of our retailers and Google sell epubs - yay. (It's often worth price comparing.) However, I still shop at the relatively new Amazon.com.au mainly because we often get UK titles before the USA - double yay.

Cheers