1. A computer-implemented method comprising: receiving one or more characteristics of a client requesting access to protected content, the protected content comprising data; determining, with at least one processor, a risk profile for the client based on the client characteristics, the risk profile reflecting a likelihood that the client is unauthorized to access the protected content; selecting, with at least one processor, first challenge characteristics or second challenge characteristics of a challenge/response test based on the risk profile; generating a challenge/response test based on the selected challenge characteristics, the generating comprising: determining a challenge phrase comprising a plurality of characters; and dividing the challenge phrase into at least two character subsets selected from the plurality of characters comprising the challenge phrase; and providing the at least two character subsets for consecutive display on the client at a predetermined frequency, wherein the first challenge characteristics and the second challenge characteristics each reflect distortion levels used to distort characters of the challenge/response test, and the first challenge characteristics reflect less character distortion than the second challenge characteristics.
1. A computer-implemented method comprising: receiving one or more characteristics of a client requesting access to protected content, the protected content comprising data; determining, with at least one processor, a risk profile for the client based on the client characteristics, the risk profile reflecting a likelihood that the client is unauthorized to access the protected content; selecting, with at least one processor, first challenge characteristics or second challenge characteristics of a challenge/response test based on the risk profile; generating a challenge/response test based on the selected challenge characteristics, the generating comprising: determining a challenge phrase comprising a plurality of characters; and dividing the challenge phrase into at least two character subsets selected from the plurality of characters comprising the challenge phrase; and providing the at least two character subsets for consecutive display on the client at a predetermined frequency, wherein the first challenge characteristics and the second challenge characteristics each reflect distortion levels used to distort characters of the challenge/response test, and the first challenge characteristics reflect less character distortion than the second challenge characteristics. 11. The computer-implemented method according to claim 1 , wherein the challenge/response test includes a challenge phrase comprising a plurality of characters, wherein the challenge phrase is divided 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.