Google: Security questions across websites are very easy to guess

FTA:

For example using a single guess an attacker would have a 19.7% success rate at guessing English-speaking users' answers for the question "Favorite food?"

… With 10 guesses an attacker would be able to guess 39% of Korean-speaking users' answers to "City of birth?"

As for English-speakers favorite food, the most common answer is, not too surprisingly, "pizza."

More:

http://bgr.com/2015/05/22/google-security-passwords-secure-easy-guess/