Believe it or not, the “possession” of certain numbers could get you into some serious trouble with the law. That’s got to be the worst answer to the prison icebreaker question “what you in for?”
It’s all to do with data security. The principle of computer encryption is largely based around very large prime numbers. An encrypted file or system is “locked” with an extremely long number. The keys to access this lock are primes numbers, which equal the lock's number if they’re multiplied together. If you don’t have access to the “keys” to open the lock, you need to find the numbers yourself. Since these numbers are so long, with thousands of digits, finding other numbers that produce them takes a very, very long time, even if you're a supercomputer, hence why it is so secure.
There is one prime number (an extremely long, unspeakable number) that was the source code to unlock the copyrighted protected systems on DVDs. Using this number, you would be able to duplicate, download, or upload the data on the DVD. Under the 1998 Digital Rights Act, it could therefore be considered a tool to get around a copyrighted protected system.
Check out this video from Wendoverproductions, which beautifully and simply explains all the ins and outs of this very complicated matter, and even mentions how finding a very long prime number can make you a lot of money.