A machine-implemented method for determining whether a to-be-analyzed software is a known malware or a variant of the known malware includes the steps of: (A) configuring a processor to execute the to-be-analyzed software, and obtain a to-be-analyzed system call sequence that corresponds to the to-be-analyzed software with reference to a plurality of system calls made in sequence as a result of executing the to-be-analyzed software; (B) configuring the processor to determine a degree of similarity between the to-be-analyzed system call sequence and a reference system call sequence that corresponds to the known malware; and (C) configuring the processor to determine that the to-be-analyzed software is neither the known malware nor a variant of the known malware when the degree of similarity determined in step (B) is not greater than a predefined similarity threshold value.