1. A method of identifying strings in an e-mail message, the method comprising: receiving an e-mail message; and executing instructions stored in memory, wherein execution of the instructions by a processor: identifies a text string in the e-mail message; determines that the identified text string in the e-mail message is not a safe string, wherein safe strings are predetermined strings stored in a database of acceptable terms and identified as legitimately present in e-mail messages; associates the text string with a guarded term from a database of guarded terms stored in memory, the guarded term being a string of special interest to a user; evaluates a cost of the association of the identified text string that dictates a probability that the identified text string is a mutation of the associated guarded term, wherein the evaluation compares similarities and differences between the identified text string and the guarded term, and wherein the evaluation assigns different penalties for the cost based on whether the mutation includes regular characters or special characters; matches the identified text string with the guarded term when the cost of association of the identified text string meets a predetermined threshold; and characterizes the e-mail message based on the matching between the identified text string and the guarded term.