»the tradition of using the phrase “Hello world!” as a test message was influenced by an example program in the book The C Programming Language. The example program from that book prints “hello, world” (without capital letters or exclamation mark), and was inherited from a 1974 Bell Laboratories internal memorandum by Brian Kernighan, Programming in C: A Tutorial«

http://en.wikipedia.org/wiki/Hello_world_program

Excellent answer, I was about to guess that it was Hello Kitty.