diff --git a/SharpSnmpLib/Security/DESPrivacyProvider.cs b/SharpSnmpLib/Security/DESPrivacyProvider.cs
index 07aa45d0..fd818401 100644
--- a/SharpSnmpLib/Security/DESPrivacyProvider.cs
+++ b/SharpSnmpLib/Security/DESPrivacyProvider.cs
@@ -30,6 +30,7 @@ namespace Lextm.SharpSnmpLib.Security
     /// </summary>
     /// <remarks>Ported from SNMP#NET PrivacyDES class.</remarks>
     [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Naming", "CA1709:IdentifiersShouldBeCasedCorrectly", MessageId = "DES", Justification = "definition")]
+    [Obsolete("DES is no longer secure. Please use a more secure provider.")]
     public sealed class DESPrivacyProvider : IPrivacyProvider
     {
         private readonly SaltGenerator _salt = new SaltGenerator();
diff --git a/SharpSnmpLib/Security/MD5AuthenticationProvider.cs b/SharpSnmpLib/Security/MD5AuthenticationProvider.cs
index 624743cc..ab2cfff5 100644
--- a/SharpSnmpLib/Security/MD5AuthenticationProvider.cs
+++ b/SharpSnmpLib/Security/MD5AuthenticationProvider.cs
@@ -26,6 +26,7 @@ namespace Lextm.SharpSnmpLib.Security
     /// <summary>
     /// Authentication provider using MD5.
     /// </summary>
+    [Obsolete("MD5 is no longer secure. Please use a more secure provider.")]
     public sealed class MD5AuthenticationProvider : IAuthenticationProvider
     {
         private const int Md5KeyCacheCapacity = 100;
diff --git a/SharpSnmpLib/Security/SHA1AuthenticationProvider.cs b/SharpSnmpLib/Security/SHA1AuthenticationProvider.cs
index 0c449853..c9947a6c 100644
--- a/SharpSnmpLib/Security/SHA1AuthenticationProvider.cs
+++ b/SharpSnmpLib/Security/SHA1AuthenticationProvider.cs
@@ -28,6 +28,7 @@ namespace Lextm.SharpSnmpLib.Security
     /// Authentication provider using SHA-1.
     /// </summary>
     [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Naming", "CA1709:IdentifiersShouldBeCasedCorrectly", MessageId = "SHA", Justification = "definition")]
+    [Obsolete("SHA-1 is no longer secure. Please use a more secure provider.")]
     public sealed class SHA1AuthenticationProvider : IAuthenticationProvider
     {
         private const int Sha1KeyCacheCapacity = 100; 
diff --git a/SharpSnmpLib/Security/TripleDESPrivacyProvider.cs b/SharpSnmpLib/Security/TripleDESPrivacyProvider.cs
index ea57de55..15648e69 100644
--- a/SharpSnmpLib/Security/TripleDESPrivacyProvider.cs
+++ b/SharpSnmpLib/Security/TripleDESPrivacyProvider.cs
@@ -28,6 +28,7 @@ namespace Lextm.SharpSnmpLib.Security
     /// Privacy provider for 3DES.
     /// </summary>
     /// <remarks>Ported from SNMP#NET Privacy3DES class.</remarks>
+    [Obsolete("3DES is no longer secure. Please use a more secure provider.")]
     [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Naming", "CA1709:IdentifiersShouldBeCasedCorrectly", MessageId = "DES", Justification = "definition")]
     public sealed class TripleDESPrivacyProvider : IPrivacyProvider
     {