Backup system work represents “the last mile” of information security (IS). To avoid data loss or damage, enterprises should execute data backup periodically to ensure the integrity and availability of such data. Additionally, due to the continuous emergence of IS incidents featuring malicious attacks in recent years, major firms in countries around the world have successively reported being under attack by ransomware viruses. In particular, small and medium enterprises (SMEs) became the potential targets of malicious attacks based on their different types of IS awareness and degrees of digitalization; therefore, IS work has become one of the essential topics with special significance for numerous SMEs. To this end, this paper studied the factors influencing SMEs’ adoption of IS backup systems in the hope that the critical decision-making behaviors of SMEs regarding the issue of IS could be learned. Practical suggestions can be made for the marketing schemes adopted by IS manufacturers concerning the planning of IS backup systems. Thus, this study used three methodological stages to address the exciting issue of IS backup systems for SMEs. In the first stage, 11 factors at two hierarchies involving three constructs influencing SMEs’ adoption of IS backup systems were summarized via a literature review. The constructs included financial consideration (FC), the IS incident, and business IS decision making (BISD-M). In the second stage, an expert questionnaire was applied; an advanced hybrid modified Delphi method (MDM) and analytic hierarchy process (AHP) with expert input were constructed to identify the sorting of overall weights based on the 11 factors included in the first stage. Following the empirical conclusions, the top three critical factors were “disaster loss amount”, “enterprise’s downtime”, and “supplier’s contractual requirements”. The conclusions of this study indicated that two factors were included in the FC construct; thus, the FC construct influenced IS the most, and the BISD-M construct took second place. In the final stage, through re-checking three actual cases, the results of this study were verified with specific respect to the FC. In conclusion, to popularize IS backup systems among SMEs and fully implement IS, manufacturers may start from the FC in the hope that the severe impact caused by IS incidents featuring malicious attacks can be slowed down and the losses encountered can be lowered. The empirical results and conclusions of this study can be used for reference by SMEs, and both theoretical and empirical foundations have been provided for further studies in academic circles; the results above also show a significant application contribution of this study.