WebAssembly has emerged as a low-level language for the web and beyond. Despite its popularity in different domains, little is known about WebAssembly binaries that occur in the wild. This paper presents a comprehensive empirical study of 8,461 unique WebAssembly binaries gathered from a wide range of sources, including source code repositories, package managers, and live websites. We study the security properties, source languages, and use cases of the binaries and how they influence the security of the WebAssembly ecosystem. Our findings update some previously held assumptions about real-world WebAssembly and highlight problems that call for future research. For example, we show that vulnerabilities that propagate from insecure source languages potentially affect a wide range of binaries (e.g., two thirds of the binaries are compiled from memory unsafe languages, such as C and C++) and that 21% of all binaries import potentially dangerous APIs from their host environment. We also show that cryptomining, which once accounted for the majority of all WebAssembly code, has been marginalized (less than 1% of all binaries found on the web) and gives way to a diverse set of use cases. Finally, 29% of all binaries on the web are minified, calling for techniques to decompile and reverse engineer WebAssembly. Overall, our results show that WebAssembly has left its infancy and is growing up into a language that powers a diverse ecosystem, with new challenges and opportunities for security researchers and practitioners. Besides these insights, we also share the dataset underlying our study, which is 58x larger than the largest previously reported benchmark.