It was expanded by Geoff Collyer in 1989 and since then has had input from many others, including Guy Harris, Chris Lowth and Eric Fischer; from late 1993 onward its maintenance has been organized by Christos Zoulas.

The OpenBSD system has its own subset implementation written from scratch, but still uses the Darwin/Zoulas collection of magic file formatted information.

It is easy to fool the program by putting a magic number into a file the content of which does not match it.

Through Ian Darwin's non-standard option -k the program does not stop after the first hit found, but looks for other matching patterns.

The -r option, which is available in some versions, causes the unprintable new line character to be displayed in its raw form rather than in its octal representation.