The digital microfluidic biochips (DMFBs) have the advantages of high precision, small consumption of samples/reagents, and high flexibility in experimental places. Nowadays, DMFB technology has been implemented in industry, such as by illumina. However, similar to the situation faced in integrated circuits, DMFBs also suffer from various security risks and end users usually know little about these security threats. Accordingly, in this paper, we propose a survey on DMFBs security in the research community. First, we prevent an overview of the attack behaviors in DMFBs and list them according to the design and manufacture flow. Then, we outline the current defense techniques and classify them into several categories according to their corresponding purposes and functions. Finally, the comparison between security threats faced in DMFBs and the corresponding defense techniques are provided and analyzed in detail, thus presenting the future research trends in DMFBs security.