We present Volleystore, a filesystem that stores data on network equipment and servers without any authorization, yet without compromising the systems that are used. This is achieved by exploiting the echo functionality present in most standard Internet protocols. Various issues concerning the design of a parasitic storage system are addressed and a practical system based on Internet Control Message Protocol (ICMP) echo messages is demonstrated. We present an analysis of storage capacity and latency limits for various configurations of the system. We also describe a proof-of-concept implementation of the system and show that one can indeed store data using Volleystore for a reasonable lengths of time. Finally, we suggest defenses against parasitic storage, both abstractly in economic terms and concretely in technical terms.