Illegal number

[1][2][3] A number may represent some type of classified information or trade secret, legal to possess only by certain authorized persons.

It allegedly assists in the decryption of any HD DVD or Blu-ray Disc released before this date.

[10] Sony later accidentally retweeted an older dongle key through its fictional Kevin Butler character.

[11] As a protest of the DeCSS case, many people created "steganographic" versions of the illegal information (i.e. hiding them in some form in flags etc.).

Some illegal numbers are so short that a simple flag (shown in the image) could be created by using triples of components as describing red-green-blue colors.

There are other contexts in which smaller numbers have run afoul of laws or regulations, or drawn the attention of authorities.