E-learning provides the opportunity for student to interact electronically with each other as well as with their teachers. This interaction can be via e-mail or on discussion board or in chat rooms. Though recognizing that the world at large will persist to use language and terminology in different ways, so the term of virtual learning environments (VLE) is used to refer the on-line interactions for a variety of kinds that take place between students and teachers. There are many software systems available that provide VLE systems. This software is in both forms, commercial and open source software (OSS). Moodle is one of the systems that have been increasingly gaining worldwide popularity in e-learning system. This paper is focused on the Moodle Architecture and comparative study of Moodle, thus we discusses comparisons between different virtual learning management systems and presents some authentication plug-in that Moodle supports. The open source learning management, LMS Moodle has been adopted by many people and organizations around the world because it offers a tightly integrated set of tools said to be designed from a social constructive perspective. Moodle has been developed under the general public license and many of its components were developed without a specific design documentation including its security services.