4.) User Mode

User-level (user-mode): On an operating system, there are fundamental two contexts a program can run in. The kernel context is within the core of the operating system, and no checks are performed to see if accesses to system resources are legal. The other context is user-level, where full access to the system is walled-off. Key point: Many network services these days now run as restricted user-level processes. This means when a remote hacker breaks into such a service, they do not get full control over the machine. They might be able to deface a webpage or cause other havoc, but they do not own the box. At this point, the intruder will need to run some sort of privilege escalation exploit in order to root the system. From Hacking-Lexicon