The only secure shared environments I would trust are jailed environments or virtualized OSes, and even then only if I could control the hardware. Even then the

The only secure shared environments I would trust are jailed environments or virtualized OSes, and even then only if I could control the hardware. Even then there have been vulnerabilities which allow virtualized OSes to access the host system (and "sideways" into other OSes), meaning even something like EC2 is potentially vulnerable. Don't trust your environment.