1. A method for securing a computing system, comprising: monitoring a program whose loaded program code comprises instructions that are loaded into memory of the computing system; and using a code cache to enforce a security policy on said program, the step of using includes: determining compliance of the instructions with the security policy; copying the instructions from the loaded program code into the code cache after the instructions are determined to comply with the security policy; and modifying instructions of the program which represent control transfers to ensure that the control transfers of the program comply with the security policy, and to ensure that the program is executed from the code cache instead of from the loaded program code.