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diff --git a/src/System.Net.TestData/readme.md b/src/System.Net.TestData/readme.md
new file mode 100644
index 000000000..e03aab3da
--- /dev/null
+++ b/src/System.Net.TestData/readme.md
@@ -0,0 +1,7 @@
+# System.Net test certificates
+
+This package contains test certificates for `System.Net` library.
+
+The TestData directory is considered obsolete. The certificates are encrypted with RC2 and triple des encryption. The pfx password is `testcertificate`.
+
+The TestDataCertificates directory contains the same pfx certificates as in TestData however they are all encrypted by triple des encryption. The pfx password is `PLACEHOLDER`.
\ No newline at end of file