9. The host computing device according to claim 8 , wherein the processor, when executing the codes to select the virus signatures candidate from the at least one text string of characters sequence, is configured to: select a test string from the at least one text string of characters sequence having the first frequency not exceeding a preset first frequency threshold and the second frequency exceeding a preset second frequency threshold; and determine that the selected text string of characters sequence as the virus signatures candidate.
8. A host computing device for obtaining at least one virus signature, the host computing device comprising: a plurality of computer files stored in one or more memory locations of the host computing device; and at least a processor with circuitry operating in conjunction with a memory storing codes of an anti-virus program, wherein the processor, when executing the code, is configured 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.