diff --git a/src/Moryx.ControlSystem/Activities/ActivityClassification.cs b/src/Moryx.ControlSystem/Activities/ActivityClassification.cs
index 7548c64..17f721d 100644
--- a/src/Moryx.ControlSystem/Activities/ActivityClassification.cs
+++ b/src/Moryx.ControlSystem/Activities/ActivityClassification.cs
@@ -15,6 +15,11 @@ namespace Moryx.ControlSystem.Activities
     [Flags]
     public enum ActivityClassification
     {
+        /// <summary>
+        /// Use in case the activity classification is unkown
+        /// </summary>
+        Unknown = 0x00,
+
         /// <summary>
         /// Default classification is production
         /// </summary>
@@ -33,6 +38,6 @@ public enum ActivityClassification
         /// <summary>
         /// Activity performs a preparation, for example for a <see cref="Production"/> activity
         /// </summary>
-        Preparation = 0x08
+        Preparation = 0x08,
     }
 }
diff --git a/src/Moryx.ControlSystem/Cells/ActivityCompleted.cs b/src/Moryx.ControlSystem/Cells/ActivityCompleted.cs
index 5d315fe..4ad1466 100644
--- a/src/Moryx.ControlSystem/Cells/ActivityCompleted.cs
+++ b/src/Moryx.ControlSystem/Cells/ActivityCompleted.cs
@@ -10,9 +10,6 @@ namespace Moryx.ControlSystem.Cells
     /// </summary>
     public class ActivityCompleted : Session, ICompletableSession
     {
-        /// <summary>
-        /// Initialize a new resource request for a certain resource
-        /// </summary>
         internal ActivityCompleted(IActivity completed, Session currentSession)
             : base(currentSession)
         {
diff --git a/src/Moryx.ControlSystem/Cells/Session.cs b/src/Moryx.ControlSystem/Cells/Session.cs
index 5f0474e..e379d73 100644
--- a/src/Moryx.ControlSystem/Cells/Session.cs
+++ b/src/Moryx.ControlSystem/Cells/Session.cs
@@ -125,6 +125,19 @@ public static ReadyToWork StartSession(ActivityClassification classification, Re
             return CreateSession(classification, type, ProcessReference.InstanceIdentity(identity), constraints);
         }
 
+
+        /// <summary>
+        /// Creates a new <see cref="Session"/> for the <paramref name="unknown"/> activity
+        /// with a new session context and marks the activity as failed.
+        /// </summary>
+        /// <param name="unknown"></param>
+        public static UnknownActivityAborted WrapUnknownActivity(IActivity unknown)
+        {
+            var wrapper = StartSession(ActivityClassification.Unknown, ReadyToWorkType.Unset, unknown.Process.Id)
+                .CompleteSequence(null, false, new long[] { });
+            return new UnknownActivityAborted(unknown, wrapper);
+        }
+
         private static ReadyToWork CreateSession(ActivityClassification classification, ReadyToWorkType type, ProcessReference reference, IConstraint[] constraints)
         {
             if (constraints == null)
diff --git a/src/Moryx.ControlSystem/Cells/UnknownActivityAborted.cs b/src/Moryx.ControlSystem/Cells/UnknownActivityAborted.cs
new file mode 100644
index 0000000..33a79ef
--- /dev/null
+++ b/src/Moryx.ControlSystem/Cells/UnknownActivityAborted.cs
@@ -0,0 +1,26 @@
+// Copyright (c) 2024, Phoenix Contact GmbH & Co. KG
+// Licensed under the Apache License, Version 2.0
+
+using Moryx.AbstractionLayer;
+
+namespace Moryx.ControlSystem.Cells
+{
+    /// <summary>
+    /// Message send by the resource managment when it aborted an activity for an 
+    /// unkown session.
+    /// </summary>
+    public class UnknownActivityAborted : ActivityCompleted
+    {
+        internal UnknownActivityAborted(IActivity aborted, Session wrapper)
+            : base(aborted, wrapper)
+        {
+            aborted.Fail();
+            AbortedActivity = aborted;
+        }
+
+        /// <summary>
+        /// Activity that was aborted
+        /// </summary>
+        public IActivity AbortedActivity { get; }
+    }
+}
diff --git a/src/Tests/Moryx.ControlSystem.Tests/ProductionSessionTests.cs b/src/Tests/Moryx.ControlSystem.Tests/ProductionSessionTests.cs
index 29f03f4..751b282 100644
--- a/src/Tests/Moryx.ControlSystem.Tests/ProductionSessionTests.cs
+++ b/src/Tests/Moryx.ControlSystem.Tests/ProductionSessionTests.cs
@@ -139,5 +139,20 @@ public void TestContinueSession(ReadyToWorkType readyToWorkType)
             Assert.AreEqual(ReadyToWorkType.Pull, readyToWork2.ReadyToWorkType);
         }
 
+        [Test]
+        public void TestUnknownActivityAborted()
+        {
+            // Arrange
+            var process = new Process { Id = 4242 };
+            var activity = new DummyActivity { Process = process };
+
+            // Act
+            var session = Session.WrapUnknownActivity(activity);
+
+            // Assert
+            Assert.That(session.AcceptedClassification, Is.EqualTo(ActivityClassification.Unknown));
+            Assert.That(session.AbortedActivity, Is.EqualTo(activity));
+            Assert.That(session.Reference.Matches(process));
+        }
     }
 }