Solution to 4:

    This is a substitution cipher. When deciphered, the plaintext is an excerpt from the Wikipedia article for "red herring", indicating that the plaintext is not important. The answer lies in the cipher's key - A=C, B=O, C=M, D=P, E=L, etc. The first 10 letters of the key spell the word "complexity".

    Since the plaintext did not contain J, the 10th letter of the alphabet, it was not explicitly clear that the 10th letter was a Y rather than two or three other possibilities. We decided that this would not be a problem, as "complexit" is hardly a compelling answer. Much to our surprise, a number of teams tried entering "complexit" as an answer!

COMPLEXITY