Chaim.b is a worm that spreads through network shares and by exploiting known Microsoft Windows vulnerabilities. It can also propagate through instant messages containing links to malicious files using the AOL Instant Messenger program. Once executed, the parasite secretly installs itself to the system. Then it runs a payload. Chaim.b opens a back door providing the attacker with unauthorized remote access to the compromised computer. The intruder can download and execute arbitrary files, manage processes, run programs, search the infected system for specific files, execute system commands and steal user passwords. The worm also allows to launch Denial of Service (Dos) attacks, run a hidden proxy, FTP or web server, scan the network for vulnerable hosts and restart the PC. Chaim.b runs on every Windows startup.