https://docs.microsoft.com/en-us/cpp/security/developer-guidance-speculative-execution

This article contains guidance for developers to assist with identifying and mitigating speculative execution side channel hardware vulnerabilities in C++ software. These vulnerabilities can disclose sensitive information across trust boundaries and can affect software that runs on processors that support speculative, out-of-order execution of instructions. This class of vulnerabilities was first described in January, 2018 and additional background and guidance can be found in Microsoft's security advisory.