Update version information in SECURITY.md

SECURITY.md

@@ -9,13 +9,16 @@ possible.
 Should a security issue arise, a fix would usually be included in a PATCH or MINOR version update,
 i.e., 2.6.1 -> 2.6.2 or 2.7.0.
 
+All 2.x.x versions should be backwards-compatible. Consider the latest 2.x.x version the recommended
+version.
+
 If you depend on an outdated version of junixsocket or need other commercial support, please reach
 out to directly to Christian Kohlschütter (email is in `pom.xml`).
 
 | Version | Supported |
 | ------- | ------------------ |
-| 2.6.x | :white_check_mark: |
-| < 2.6.x | Commercial support available |
+| 2.9.x | :white_check_mark: |
+| < 2.9.x | Commercial support available |
 | < 2.0 | :x: |
 
 ## Reporting a Vulnerability