Machine　learning　or　data　mining　method　can　identify　new　or　unknown　malicious　executables　with　some　degree　of　success.　Feature　selection　is　a　key　to　applying　data　mining　or　machine　learning　to　detect　malicious　executables.　In　order　to　improve　detecting　accuracy,　a　new　method　of　extracting　most　representative　features　is　purposed.　The　new　classifier　based　on　strings　achieves　has　high　detection　rates　and　can　be　expected　to　perform　well　in　real-world　conditions.