TSMC, the largest semiconductor contract manufacturer in the world, is one of ASML's chief customers. It isn't clear how ASML could remotely disable equipment sitting in a factory in Taiwan, but it is understood that the huge and complex photolithography machines require regular servicing and maintenance to keep them running. According to Bloomberg, the company could, as part of a software update applied during maintenance, remotely force a shutdown, which would act as a kill switch.