Microfluidic routing fabrics, or crossbars, based on transposer primitives provide benefits in manufacturability, performance, and on-the-fly reconfigurability. Many applications in microfluidics, such as DNA barcoding for single-cell analysis, are expected to benefit from these new devices. However, the control of these critical devices poses new security questions that may impact the functional integrity of a microbiology application. This paper explores the many security implications of microfluidic crossbars that directly result from their structure, programmability and use in critical applications. We analyze security performance using new metrics describing how fluids can be 'scattered' to incorrect locations under fault-injection attacks, and from these derive a probability model describing the likelihood of a successful attack. We present a case study of a recently described routing fabric proposed for use in a hybrid DNA barcoding platform, and discuss how fabric designers can improve security through architectural choices.