17. The non-transitory computer-readable storage medium according to claim 15 , wherein the first frequency at which each of the at least one text string of characters sequence occurs in the non-virus sample set is determined by the instructions, when executed by the processor, causing the host computer device to: obtain a number of non-virus samples of the non-virus sample set containing each of the at least one text string of characters sequence; and calculate the first frequency at which each of the at least one text string of characters sequence occurs in the non-virus sample set according to the number of non-virus samples containing each of the at least one text string of characters sequence.
15. A non-transitory computer-readable storage medium storing instructions that, when executed by a processor of a host computer device, causes the host computer device to: obtain at least one text string of characters sequence contained in program code lines of virus samples of a virus sample set; select a virus signatures candidate from the at least one text string of characters sequence according to a first frequency at which each of the at least one text string of characters sequence occurs in program code lines of non-virus samples of a non-virus sample set, and a second frequency at which each of the at least one text string of characters sequence occurs in the program code lines of virus samples of the virus sample set; calculate an information entropy of the virus signatures candidate, the information entropy consisting of a value calculated according to: a number of virus samples among the virus sample set containing the virus signatures candidate, a number of virus samples among the virus sample set not containing the virus signatures candidate, a number of non-virus samples among the non-virus sample set containing the virus signatures candidate, and a number of non-virus samples among the non-virus sample set not containing the virus signatures candidate; and determine whether the virus signatures candidate qualifies as a virus signature according to the calculated information entropy.