The illegal prime posting on reddit was guaranteed to capture my attention - it combines elements of both intellectual property and mathematics.
As a mind game, this one looks fun. Since it is illegal in the US of A to possess code that defeats encryption schemes that protect digital media (a la the lovely DMCA) some hackers tried thinking of some interesting loopholes. The one they have come up with takes advantage of the behaviour of at least one version of gzip - to ignore bytes after the end of a null terminated compressed file. They generated two large prime numbers that represents the DeCSS algorithm that can unlock the encryption used to protect DVD media. Unzip one number and voila! - you get DeCSS C code. Unzip another and you get directly executable code.
Now, surely knowledge of a prime number is not considered a crime? Certainly intellectual property law sees numbers (and mathematics in general) as "elements of nature", beyond copyright or patent protection, and belonging to everyone. So far, it doesn't look like this has been tested in court. Best guess is that possession of the number would not be considered illegal, but some interpretations (like the DeCSS source code) would be.
I wonder if anyone has patented this idea yet [evil grin]...
Illegal Prime [Wikipedia]