A hijacked host works for somebody else, without the owner knowing it.

This occurs when a trojan has invaded the computer as a result of a security exposure. For example, the machine may have been connected to the Internet while it had a trivial password.

A hijacker breaks into the system by applying the hundred most frequently used passwords to the “root” administrator ID, and one of them matched. He has installed the trojan, and it will abuse the host by using its computing resources and its bandwidth.

Choose your password well, protect your server's root from being accessed, as well as take care to secure your server.