Psst . . . What starts with "09f911", ends with "35688c0", and has a whole lot of other numbers in between? Stumped? I'm afraid I can't tell you the answer, because that would be against the law.
You can have prime numbers, real numbers, imaginary numbers, irrational numbers, and, ever since the movie industry decided to wage war on the internet, you can also have illegal numbers. It all started in 1999 when a Norwegian hacker called Jon Johansen created DeCSS, a program that unravelled the "content scrambling system" intended to limit the kinds of machines on which DVDs could be played, so that he could watch them on his Linux computer.
As the DeCSS code began to circulate among other Linux users, a coding zine, 2600: the hacker quarterly, picked up the story and linked to the code online. Thanks to the Digital Millennium Copyright Act (DMCA) - the then nascent US law that renders illegal the circulation of such copyright circumvention tools - this was enough to get the magazine taken to court by the DVD Copy Control Association. Hackers worldwide were outraged, and began to protest the only way they knew how - by wearing T-shirts.
Except that these T-shirts, which had the program code written on them in full, were designed to make a point about free speech. You can't make numbers illegal, was the message: what are you going to do - throw me in jail for wearing a T-shirt? And it wasn't just clothes. The gallery of CSS descramblers, still lovingly maintained on the Carnegie Mellon School of Computer Science website, includes the DeCSS code interpreted as haiku, as music, drama and even square dance. Of course, all this activity kept DeCSS slap bang in the public sphere, such that it is still employed by Linux users to watch DVDs.
Fast-forward to today, and it seems the film-making industry has learned nothing from the DeCSS fiasco. Last year, the copy protection software that should cover the next generation of high-definition and Blu-ray DVDs was broken by hackers within weeks of its launch. They then made public the 16-byte hexadecimal key - the "illegal number" alluded to in the first paragraph of this column - needed to unlock the technology.
Instead of questioning how a system that had had millions invested in it might be so easily trumped, the Advanced Access Content System Licence Administrator, together with the Motion Picture Association of America, decided to dust off the DMCA and stop anyone from publishing the key. And can you guess what happened next?
That's right - you can now buy the latest illegal number on a T-shirt, listen to it as music; you can even become its friend on Facebook. Those who cannot remember the past are indeed condemned to repeat it. The movie industry has again ensured that the way to crack its codes will go down in hacker history.