This paper presents secure program partitioning, a language-based technique for protecting confidential data during computation in distributed systems containing mutually untrusted hosts. Confidentiality and integrity policies can be expressed by annotating programs with security types that constrain information flow; these programs can then be partitioned automatically to run securely on heterogeneously trusted hosts. The resulting communicating subprograms collectively implement the original program, yet the system as a whole satisfies the security requirements of participating principals without requiring a universally trusted host machine. The experience in applying this methodology and the performance of the resulting distributed code suggest that this is a promising way to obtain secure distributed computation. This Technical Report is an expanded version of the published paper ``Untrusted Hosts and Confidentiality: Secure Program Partitioning.'' The main difference between the two is Appendix A, which contains a correctness proof for the control-transfer protocols described in Section 5.