Prevention and detection of plagiarism have formed the basis for many research projects, but student perceptions on plagiarism are arguably not well understood, and this is particularly true in the computing disciplines. This paper considers two aspects of the student experience, (i) the types of plagiaristic activity that students engage in, and (ii) the specific understanding of what plagiarism means for students who write computer programs. In a recent study we classified types of plagiarism in computing, collecting data from two sources: published material (books, published papers, web sites), and on-line formative quizzes and questionnaires used by universities to test student knowledge of what constitutes plagiarism. Facet analysis was used to categorise the data into four initial categories (sources, actions, material, extrinsic). Further analysis suggested a refinement to six categories and 23 sub-categories which directly relate to the computing disciplines. In a further study we analysed data collected from 18 UK institutions via an online questionnaire, in which over 700 computing students were invited to scrutinise fifteen scenarios which may (or may not) contain plagiarism, and to identify which they thought did contain plagiarism. The results of this study suggest that there are certain types of plagiaristic activity which are poorly understood, and demographic factors which correlate with student understanding. This paper summarises and compares the results of these two studies and reflects on the implications for educating computing students about how they should avoid plagiarism.