Metasploit Framework 3.3 Released

It's a network security tool used for exploiting security holes in Windows systems in order to inject a remote control payload. It does have white-hat utility, but my sense is that it's mostly used for grey and black-hat activities.

Unlike the usual "script kiddie" Linux rootkits, it is largely focused in exploration and control of a single machine, but the building blocks Metasploit provides could easily be used to construct botnets, especially in dense networks like college campuses or medium-sized businesses without a strong IT security focus.

See it as a toolbox to build programs that attack other systems. Those programs are often called 'exploit', as they exploit a problem in an other system. During exploit development some tasks tend to be always the same. For example, creating a network connection to the target. Metasploit enables you to write your exploit in a way that you do not need to reinvent the wheel and makes certain parts interchangeable like the 'payload' (code to be executed on the attacked system).