The term open source means that the source code of the program is available to the public. Source code is computer code as written by humans and that is understandable by humans. Source code is compiled into machine code that is processed by a computer. Machine code is, in general, not understandable by humans and cannot be modified. In a closed source project, say Microsoft Office, the source code is highly protected and only available to trusted employees and carefully vetted contractors. The source code is very well protected. Only those trusted programmers can make changes to a closed source project. With open source, anyone can obtain the source code from the open source project's Web site. Programmers alter or add to this code depending on their interests and goals. In most cases, programmers can incorporate open source code into their own projects. They may be able to resell those projects depending on the type of license agreement the project uses. Open source succeeds because of collaboration. A programmer examines the source code and identifies a need or project that seems interesting. He or she then creates a new feature, redesigns or reprograms an existing feature, or fixes a known problem. That code is then sent to others in the open source project who then evaluate the quality and merits of the work and add it to the product, if appropriate.