Techniques for improving the security of nonvolatile memory such as magnetic random access memory (MRAM) are provided. In one aspect, a method of operating a nonvolatile memory chip is provided. The method includes: overwriting data stored on the nonvolatile memory chip automatically upon the nonvolatile memory chip being powered on. For example, all bits in the nonvolatile memory chip can be written to either i) a predetermined data state (e.g., a logic 1 or a logic 0) or ii) a random data state. A system is also provided that includes: a nonvolatile memory chip; and a writing circuit configured to overwrite data stored on the nonvolatile memory chip automatically upon the nonvolatile memory chip being powered on.