Nugache is a rapidly spreading Internet worm that propagates by e-mail, via instant messages, through unprotected network shares, and by exploiting known Windows vulnerabilities. Once executed, the parasite secretly installs itself to the system and runs a spreading routine. It distributes itself through e-mail messages with infected files attached, attempts to exploit remote vulnerable computers, and uses AOL Instant Messenger or Windows Messenger to send malicious messages to user contacts. Then the worm runs a payload. It opens a back door providing the attacker with unauthorized remote access to the compromised computer. The intruder can perform denial of service (DoS) attacks, run a hidden web server and access a predefined FTP server. Nugache secretly runs on every Windows startup.