The outbreak of Covid-19 pandemic in early 2020 has forced the general educational system in many countries to switch to online learning, leading to the fact that tests have also been moved to remote online exams. With this test method, the problem of academic dishonesty while taking exams of high school students has emerged as an issue that needs to be studied. Therefore, this study explores the pervasiveness and legitimacy of nine academic dishonesty of Vietnamese high school students participating in remote online exams during Covid-19 pandemic, divided into two groups: cheating (7 acts) and plagiarism (2 acts). To achieve the research objectives, descriptive statistics, ANOVA, Spearman, and Welch correlation analysis were used to analyse the data. The analysis results show that, in general, the pervasiveness of dishonest acts is assessed at a fairly common level, while the legitimacy of these acts is assessed at a fairly illegal level. Regarding gender, there is a difference in the assessment of the pervasiveness of some dishonest acts between male and female students, and there is a slight difference in the assessment of the legitimacy of dishonest acts between male and female students. Regarding the relationship between pervasiveness and legitimacy of the behavioral groups, the analysis results show a positive correlation generally. The research results are not only useful evidence for Vietnamese educators and managers about the issue of academic dishonesty in remote online exams conducted in the context of social distancing due to Covid-19 pandemic, but also provide suggestions for improving the quality of remote online exams by reducing academic dishonesty.