Many networked applications could benefit from executing closer to the data or services with which they interact. By doing this they may be able to circumvent long communication latencies or avoid transferring data over congested or expensive network links. However, no public infrastructure currently exists that enables this. We propose a system that can execute code supplied by an untrusted user, yet can charge this user for all resources consumed by the computation. Such servers could be deployed at strategic locations throughout the Internet, enabling network users such as content providers to distribute components of their applications in a manner that is both efficient and economical. We call such a server a Xenoserver1 . This paper discusses the construction of such a system, examining how accounting, billing, and quality of service provision can be achieved.