What Is This File?

A colleague forwards you a file with an ordinary-looking document name and asks whether it is safe to open. The name says one thing, but names are only labels that anyone can change. Your job is to work out what the file really is before anything else happens to it.

Open the specimen in the viewer and look at the first bytes: a plain-text banner, followed by the file's magic bytes, a short signature that formats use to announce themselves. Compare the signature and the plain-text banner with the file's extension, then state the true type. Do not rely on the extension, the icon or the file size.

Everything here is an inert teaching specimen made by us in our own format: it contains no working code, and every host and address in it is fictional. Nothing in it can run, and the lab is finished entirely in your browser. You can download the file to look at it in your own hex viewer if you wish, but you never need to.

Submit the file type the specimen really is, as the lab's answer box asks for it, and the flag follows.