There are provided a method and system for determining the validity of a command, which includes: a first step of receiving a command including a predetermined query from a terminal of a user; a second step of generating log information associated with the command, in which the log information includes at least one of the query included in the command, input time point information on a time point of inputting the command, and a network address of the terminal; a third step of recording the log information in a log database; a fourth step of calculating a first determination result with respect to the validity of the command according to a predetermined first determination standard; a fifth step of including identification information determined according to the first determination result in the log information and recording in the log database; a sixth step of periodically searching for log information recorded for a first period with reference to the log database; and a seventh step of determining again the validity of the command by using the searched log information according to a predetermined second determination standard and calculating a second determination result.