1. A computer-implemented method comprising: receiving a request for protected content from a client, the protected content comprising data; determining a challenge phrase comprising a plurality of characters; dividing, using a computer processor, the challenge phrase into at least two character subsets selected from the plurality of characters comprising the challenge phrase, each of the at least two character subsets comprising less than all of the characters comprising the challenge phrase; sending the at least two character subsets to the client in response to the request; and receiving, from the client and in response to the at least two character subsets, an answer to the challenge phrase, wherein access to the protected content is limited based on whether the answer correctly solves the challenge phrase.