Rustock.b is a stealthy backdoor that provides the attacker with unauthorized remote access to the compromised computer. Although the parasite does not allow the intruder to control the infected PC, it converts the system to a hidden proxy used for certain malicious purposes, such as sending e-mail spam. The backdoor may also hijack the web browser and redirect the user to undesirable web sites. Furthermore, it may collect certain system information, download and install the ICQ 5 program without user knowledge and consent. Rustock.b uses an integrated rootkit to hide its registry entries, files and active processes. It is able to bypass firewalls and avoid detection by popular rootkit detectors and removers. The backdoor runs as a service on every Windows startup.