Assembly: System (in System.dll)
This property selects the version of the Secure Sockets Layer (SSL) or Transport Layer Security (TLS) protocol to use for new connections that use the Secure Hypertext Transfer Protocol (HTTPS) scheme only; existing connections are not changed.
Note that no default value is listed for this property, on purpose. The security landscape changes constantly, and default protocols and protection levels are changed over time in order to avoid known weaknesses. Defaults will vary depending on individual machine configuration, and on which software is installed, and on which patches have been applied.
Your code should never implicitly depend on using a particular protection level, or on the assumption that a given security level is used by default. If your app depends on the use of a particular security level, you must explicitly specify that level and then check to be sure that it is actually in use on the established connection. Further, your code should be designed to be robust in the face of changes to which protocols are supported, as such changes are often made with little advance notice in order to mitigate emerging threats.
The .NET Framework 4.6 includes a new security feature that blocks insecure cipher and hashing algorithms for connections. Applications using TLS/SSL through APIs such as HttpClient, HttpWebRequest, FTPClient, SmtpClient, SslStream, etc. and targeting .NET Framework 4.6 get the more-secure behavior by default.
Developers may want to opt out of this behavior in order to maintain interoperability with their existing SSL3 services OR TLS w/ RC4 services. This article explains how to modify your code so that the new behavior is disabled.
Available since 1.1