Chaim is an Internet worm that spreads 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 opens a back door providing the attacker with unauthorized remote access to the compromised computer. The intruder can start the worm’s spreading routine, download and upload arbitrary files. Chaim disables the Windows Firewall, stops essential Windows services, lowers system security settings and prevents important updates from being installed. It can also download from the Internet and execute potentially malicious files. The worm runs as a service on every Windows startup.