1. A system comprising: a weak string predictor embodied via executable instructions stored on a machine readable storage device; and at least one device processor configured to execute at least a portion of the executable instructions stored on the machine readable storage device, the weak string predictor including: a prefix acquisition component configured to obtain a current prefix character string received from a user input device, representing a prefix of a proposed password; a prediction generator configured to determine a prediction of a most likely next character of the proposed password based on applying a set of heuristics to the current prefix character string; and a response generator configured to determine a response indicating an impact on a security strength of the proposed password, based on a selection of the predicted most likely next character, and to initiate a display of weakness attributes of a plurality of candidate passwords that include the current prefix character string, with the predicted most likely next character as a next character following the current prefix character string, included in each of the plurality of candidate passwords, the weakness attributes stating reasons for weakness of each of the plurality of candidate passwords, the response generator configured to initiate at least partial blocking of input to the user input device that is associated with current input of the predicted most likely next character, the response generator further configured to initiate a display of the predicted most likely next character of the proposed password, indicating the impact on the security strength of the proposed password.