Host computer systems automatically detect malicious code. The host computer systems automatically generate and send malicious code packets of the malicious code to a local analysis center (LAC) computer system. Based on the received malicious code packets, the LAC computer system provides a signature update to a network intrusion detection system. Further, the LAC computer system also automatically sends malicious code signatures of the malicious code to a global analysis center. In this manner, the spread of the malicious code is rapidly detected and prevented.