The establishment of an online community is widely held as the most important prerequisite for successful course completion and depends on an interaction between a peer group and a facilitator. Beaudoin reasoned that online students sometimes engage and learn even when not taking part in online discussions. The context of this study was an online course on web-based education for a Masters degree in computer-integrated education at the University of Pretoria. We used a mixed methodology approach to investigate how online activity and discussion postings relate to learning and course completion. We also investigated how student collaborative behaviour and integration into the community related to success. Although the quantitative indices measured showed highly significant differences between the stratifications of student performance, there were notable exceptions unexplained by the trends. The class harboured a well-functioning online learning community. We also uncovered the discontent students in the learning community felt for invisible students who were absent without reason from group assignments or who made shallow and insufficient contributions. Student online visibility and participation can take many forms, like read-only participants who skim over or deliberately harvest others' discussions. Other students can be highly visible without contributing. Students who anticipate limited access due to poor connectivity, high costs or other reasons can manage their log-in time effectively and gain maximum benefit. Absent and seldom contributing students risk forsaking the benefits of the virtual learning community. High quality contributions rather than quantity builds trust among mature students. We suggest how to avoid read-only-participation: communicate the required number of online classroom postings; encourage submission of high quality, thoughtful postings; grade discussions and give formative feedback; award individual grades for group projects and rotate members of groups; augment facilitator communication with Internet-independent media to convey important information. Read-only-participants disrupt the formation of a virtual community of learners and compromise learning. (Contains 2 tables and 1 figure.)