A rootkit is often used to hide utilities. These are often used to abuse a compromised system, and often include so-called "backdoors" to help the attacker subsequently access the system more easily. For example, the rootkit may hide an application that spawns a shell when the attacker connects to a particular network port on the system. Kernel rootkits may include similar functionality. A backdoor may also allow processes started by a non-privileged user to execute functions normally reserved for the administrator/superuser. All sorts of other tools useful for abuse can be hidden using rootkits. This includes tools for further attacks against computer systems which the compromised system communicates with, such as sniffers and keyloggers. A possible abuse is to use a compromised computer as a staging ground for further abuse (see zombie computer). This is often done to make the abuse appear to originate from the compromised system or network instead of the attacker. Tools for this can include denial-of-service attack tools, tools to relay chat sessions, and e-mail spam attacks. A major use for rootkits is allowing the programmer of the rootkit to see and access user names and log-in information for sites that require them. The programmer of the rootkit can store unique sets of log-in information from many different computers. This makes the rootkits extremely hazardous, as it allows Trojans to access this personal information while the rootkit covers it up. There are presently five different kinds of rootkits: firmware, virtualized, kernel, library and application level kits.