diff --git a/libraries/entities/src/EntityItem.cpp b/libraries/entities/src/EntityItem.cpp
index e1ede9192a..dc871e655f 100644
--- a/libraries/entities/src/EntityItem.cpp
+++ b/libraries/entities/src/EntityItem.cpp
@@ -276,6 +276,7 @@ OctreeElement::AppendState EntityItem::appendEntityData(OctreePacketData* packet
         APPEND_ENTITY_PROPERTY(PROP_NAME, getName());
         APPEND_ENTITY_PROPERTY(PROP_LOCKED, getLocked());
         APPEND_ENTITY_PROPERTY(PROP_USER_DATA, getUserData());
+        APPEND_ENTITY_PROPERTY(PROP_PRIVATE_USER_DATA, getPrivateUserData());
         APPEND_ENTITY_PROPERTY(PROP_HREF, getHref());
         APPEND_ENTITY_PROPERTY(PROP_DESCRIPTION, getDescription());
         APPEND_ENTITY_PROPERTY(PROP_POSITION, getLocalPosition());
@@ -812,6 +813,7 @@ int EntityItem::readEntityDataFromBuffer(const unsigned char* data, int bytesLef
     READ_ENTITY_PROPERTY(PROP_NAME, QString, setName);
     READ_ENTITY_PROPERTY(PROP_LOCKED, bool, setLocked);
     READ_ENTITY_PROPERTY(PROP_USER_DATA, QString, setUserData);
+    READ_ENTITY_PROPERTY(PROP_PRIVATE_USER_DATA, QString, setPrivateUserData);
     READ_ENTITY_PROPERTY(PROP_HREF, QString, setHref);
     READ_ENTITY_PROPERTY(PROP_DESCRIPTION, QString, setDescription);
     {   // When we own the simulation we don't accept updates to the entity's transform/velocities
@@ -1331,6 +1333,7 @@ EntityItemProperties EntityItem::getProperties(const EntityPropertyFlags& desire
     COPY_ENTITY_PROPERTY_TO_PROPERTIES(name, getName);
     COPY_ENTITY_PROPERTY_TO_PROPERTIES(locked, getLocked);
     COPY_ENTITY_PROPERTY_TO_PROPERTIES(userData, getUserData);
+    COPY_ENTITY_PROPERTY_TO_PROPERTIES(privateUserData, getPrivateUserData);
     COPY_ENTITY_PROPERTY_TO_PROPERTIES(href, getHref);
     COPY_ENTITY_PROPERTY_TO_PROPERTIES(description, getDescription);
     COPY_ENTITY_PROPERTY_TO_PROPERTIES(position, getLocalPosition);
@@ -1479,6 +1482,7 @@ bool EntityItem::setProperties(const EntityItemProperties& properties) {
     SET_ENTITY_PROPERTY_FROM_PROPERTIES(name, setName);
     SET_ENTITY_PROPERTY_FROM_PROPERTIES(locked, setLocked);
     SET_ENTITY_PROPERTY_FROM_PROPERTIES(userData, setUserData);
+    SET_ENTITY_PROPERTY_FROM_PROPERTIES(privateUserData, setPrivateUserData);
     SET_ENTITY_PROPERTY_FROM_PROPERTIES(href, setHref);
     SET_ENTITY_PROPERTY_FROM_PROPERTIES(description, setDescription);
     SET_ENTITY_PROPERTY_FROM_PROPERTIES(position, setPosition);
@@ -3120,6 +3124,20 @@ void EntityItem::setUserData(const QString& value) {
     });
 }
 
+QString EntityItem::getPrivateUserData() const {
+    QString result;
+    withReadLock([&] {
+        result = _privateUserData;
+    });
+    return result;
+}
+
+void EntityItem::setPrivateUserData(const QString& value) {
+    withWriteLock([&] {
+        _privateUserData = value;
+    });
+}
+
 // Certifiable Properties
 #define DEFINE_PROPERTY_GETTER(type, accessor, var) \
 type EntityItem::get##accessor() const {            \
diff --git a/libraries/entities/src/EntityItem.h b/libraries/entities/src/EntityItem.h
index 29a1a8d73c..90a1d82253 100644
--- a/libraries/entities/src/EntityItem.h
+++ b/libraries/entities/src/EntityItem.h
@@ -331,6 +331,9 @@ public:
     QString getUserData() const;
     virtual void setUserData(const QString& value); // FIXME: This is suspicious
 
+    QString getPrivateUserData() const;
+    void setPrivateUserData(const QString& value);
+
     // FIXME not thread safe?
     const SimulationOwner& getSimulationOwner() const { return _simulationOwner; }
     void setSimulationOwner(const QUuid& id, uint8_t priority);
@@ -641,6 +644,7 @@ protected:
     bool _dynamic { ENTITY_ITEM_DEFAULT_DYNAMIC };
     bool _locked { ENTITY_ITEM_DEFAULT_LOCKED };
     QString _userData { ENTITY_ITEM_DEFAULT_USER_DATA };
+    QString _privateUserData{ ENTITY_ITEM_DEFAULT_PRIVATE_USER_DATA };
     SimulationOwner _simulationOwner;
     bool _shouldHighlight { false };
     QString _name { ENTITY_ITEM_DEFAULT_NAME };
diff --git a/libraries/entities/src/EntityItemProperties.cpp b/libraries/entities/src/EntityItemProperties.cpp
index 2b738bc4e7..86f293f2ea 100644
--- a/libraries/entities/src/EntityItemProperties.cpp
+++ b/libraries/entities/src/EntityItemProperties.cpp
@@ -487,6 +487,7 @@ EntityPropertyFlags EntityItemProperties::getChangedProperties() const {
     CHECK_PROPERTY_CHANGE(PROP_NAME, name);
     CHECK_PROPERTY_CHANGE(PROP_LOCKED, locked);
     CHECK_PROPERTY_CHANGE(PROP_USER_DATA, userData);
+    CHECK_PROPERTY_CHANGE(PROP_PRIVATE_USER_DATA, privateUserData);
     CHECK_PROPERTY_CHANGE(PROP_HREF, href);
     CHECK_PROPERTY_CHANGE(PROP_DESCRIPTION, description);
     CHECK_PROPERTY_CHANGE(PROP_POSITION, position);
@@ -818,6 +819,8 @@ EntityPropertyFlags EntityItemProperties::getChangedProperties() const {
  *     which you can manipulate the properties of, and use <code>JSON.stringify()</code> to convert the object into a string to 
  *     put in the property.
  *
+ * @property {string} privateUserData="" - Like userData, but only accessible by the Entity Server Scripts.
+ *
  * @property {string} script="" - The URL of the client entity script, if any, that is attached to the entity.
  * @property {number} scriptTimestamp=0 - Intended to be used to indicate when the client entity script was loaded. Should be 
  *     an integer number of milliseconds since midnight GMT on January 1, 1970 (e.g., as supplied by <code>Date.now()</code>. 
@@ -1591,6 +1594,7 @@ QScriptValue EntityItemProperties::copyToScriptValue(QScriptEngine* engine, bool
     COPY_PROPERTY_TO_QSCRIPTVALUE(PROP_NAME, name);
     COPY_PROPERTY_TO_QSCRIPTVALUE(PROP_LOCKED, locked);
     COPY_PROPERTY_TO_QSCRIPTVALUE(PROP_USER_DATA, userData);
+    COPY_PROPERTY_TO_QSCRIPTVALUE(PROP_PRIVATE_USER_DATA, privateUserData);
     COPY_PROPERTY_TO_QSCRIPTVALUE(PROP_HREF, href);
     COPY_PROPERTY_TO_QSCRIPTVALUE(PROP_DESCRIPTION, description);
     COPY_PROPERTY_TO_QSCRIPTVALUE(PROP_POSITION, position);
@@ -1999,6 +2003,7 @@ void EntityItemProperties::copyFromScriptValue(const QScriptValue& object, bool
     COPY_PROPERTY_FROM_QSCRIPTVALUE(name, QString, setName);
     COPY_PROPERTY_FROM_QSCRIPTVALUE(locked, bool, setLocked);
     COPY_PROPERTY_FROM_QSCRIPTVALUE(userData, QString, setUserData);
+    COPY_PROPERTY_FROM_QSCRIPTVALUE(privateUserData, QString, setPrivateUserData);
     COPY_PROPERTY_FROM_QSCRIPTVALUE(href, QString, setHref);
     COPY_PROPERTY_FROM_QSCRIPTVALUE(description, QString, setDescription);
     COPY_PROPERTY_FROM_QSCRIPTVALUE(position, vec3, setPosition);
@@ -2288,6 +2293,7 @@ void EntityItemProperties::merge(const EntityItemProperties& other) {
     COPY_PROPERTY_IF_CHANGED(name);
     COPY_PROPERTY_IF_CHANGED(locked);
     COPY_PROPERTY_IF_CHANGED(userData);
+    COPY_PROPERTY_IF_CHANGED(privateUserData);
     COPY_PROPERTY_IF_CHANGED(href);
     COPY_PROPERTY_IF_CHANGED(description);
     COPY_PROPERTY_IF_CHANGED(position);
@@ -2573,6 +2579,7 @@ bool EntityItemProperties::getPropertyInfo(const QString& propertyName, EntityPr
         ADD_PROPERTY_TO_MAP(PROP_NAME, Name, name, QString);
         ADD_PROPERTY_TO_MAP(PROP_LOCKED, Locked, locked, bool);
         ADD_PROPERTY_TO_MAP(PROP_USER_DATA, UserData, userData, QString);
+        ADD_PROPERTY_TO_MAP(PROP_PRIVATE_USER_DATA, PrivateUserData, privateUserData, QString);
         ADD_PROPERTY_TO_MAP(PROP_HREF, Href, href, QString);
         ADD_PROPERTY_TO_MAP(PROP_DESCRIPTION, Description, description, QString);
         ADD_PROPERTY_TO_MAP(PROP_POSITION, Position, position, vec3);
@@ -3047,6 +3054,7 @@ OctreeElement::AppendState EntityItemProperties::encodeEntityEditPacket(PacketTy
             APPEND_ENTITY_PROPERTY(PROP_NAME, properties.getName());
             APPEND_ENTITY_PROPERTY(PROP_LOCKED, properties.getLocked());
             APPEND_ENTITY_PROPERTY(PROP_USER_DATA, properties.getUserData());
+            APPEND_ENTITY_PROPERTY(PROP_PRIVATE_USER_DATA, properties.getPrivateUserData());
             APPEND_ENTITY_PROPERTY(PROP_HREF, properties.getHref());
             APPEND_ENTITY_PROPERTY(PROP_DESCRIPTION, properties.getDescription());
             APPEND_ENTITY_PROPERTY(PROP_POSITION, properties.getPosition());
@@ -3530,6 +3538,7 @@ bool EntityItemProperties::decodeEntityEditPacket(const unsigned char* data, int
     READ_ENTITY_PROPERTY_TO_PROPERTIES(PROP_NAME, QString, setName);
     READ_ENTITY_PROPERTY_TO_PROPERTIES(PROP_LOCKED, bool, setLocked);
     READ_ENTITY_PROPERTY_TO_PROPERTIES(PROP_USER_DATA, QString, setUserData);
+    READ_ENTITY_PROPERTY_TO_PROPERTIES(PROP_PRIVATE_USER_DATA, QString, setPrivateUserData);
     READ_ENTITY_PROPERTY_TO_PROPERTIES(PROP_HREF, QString, setHref);
     READ_ENTITY_PROPERTY_TO_PROPERTIES(PROP_DESCRIPTION, QString, setDescription);
     READ_ENTITY_PROPERTY_TO_PROPERTIES(PROP_POSITION, vec3, setPosition);
@@ -3941,6 +3950,7 @@ void EntityItemProperties::markAllChanged() {
     _nameChanged = true;
     _lockedChanged = true;
     _userDataChanged = true;
+    _privateUserDataChanged = true;
     _hrefChanged = true;
     _descriptionChanged = true;
     _positionChanged = true;
@@ -4303,6 +4313,9 @@ QList<QString> EntityItemProperties::listChangedProperties() {
     if (userDataChanged()) {
         out += "userData";
     }
+    if (privateUserDataChanged()) {
+        out += "privateUserData";
+    }
     if (hrefChanged()) {
         out += "href";
     }
diff --git a/libraries/entities/src/EntityItemProperties.h b/libraries/entities/src/EntityItemProperties.h
index 0142f42536..af945a89de 100644
--- a/libraries/entities/src/EntityItemProperties.h
+++ b/libraries/entities/src/EntityItemProperties.h
@@ -180,6 +180,7 @@ public:
     DEFINE_PROPERTY_REF(PROP_NAME, Name, name, QString, ENTITY_ITEM_DEFAULT_NAME);
     DEFINE_PROPERTY(PROP_LOCKED, Locked, locked, bool, ENTITY_ITEM_DEFAULT_LOCKED);
     DEFINE_PROPERTY_REF(PROP_USER_DATA, UserData, userData, QString, ENTITY_ITEM_DEFAULT_USER_DATA);
+    DEFINE_PROPERTY_REF(PROP_PRIVATE_USER_DATA, PrivateUserData, privateUserData, QString, ENTITY_ITEM_DEFAULT_PRIVATE_USER_DATA);
     DEFINE_PROPERTY_REF(PROP_HREF, Href, href, QString, "");
     DEFINE_PROPERTY_REF(PROP_DESCRIPTION, Description, description, QString, "");
     DEFINE_PROPERTY_REF_WITH_SETTER(PROP_POSITION, Position, position, glm::vec3, ENTITY_ITEM_ZERO_VEC3);
@@ -607,6 +608,7 @@ inline QDebug operator<<(QDebug debug, const EntityItemProperties& properties) {
     DEBUG_PROPERTY_IF_CHANGED(debug, properties, Locked, locked, "");
     DEBUG_PROPERTY_IF_CHANGED(debug, properties, Textures, textures, "");
     DEBUG_PROPERTY_IF_CHANGED(debug, properties, UserData, userData, "");
+    DEBUG_PROPERTY_IF_CHANGED(debug, properties, PrivateUserData, privateUserData, "");
     DEBUG_PROPERTY_IF_CHANGED(debug, properties, SimulationOwner, simulationOwner, SimulationOwner());
     DEBUG_PROPERTY_IF_CHANGED(debug, properties, Text, text, "");
     DEBUG_PROPERTY_IF_CHANGED(debug, properties, LineHeight, lineHeight, "");
diff --git a/libraries/entities/src/EntityItemPropertiesDefaults.h b/libraries/entities/src/EntityItemPropertiesDefaults.h
index be3c566724..cc12eb37b4 100644
--- a/libraries/entities/src/EntityItemPropertiesDefaults.h
+++ b/libraries/entities/src/EntityItemPropertiesDefaults.h
@@ -28,6 +28,7 @@ const QVector<glm::vec3> ENTITY_ITEM_DEFAULT_EMPTY_VEC3_QVEC = QVector<glm::vec3
 
 const bool ENTITY_ITEM_DEFAULT_LOCKED = false;
 const QString ENTITY_ITEM_DEFAULT_USER_DATA = QString("");
+const QString ENTITY_ITEM_DEFAULT_PRIVATE_USER_DATA = QString("");
 const QUuid ENTITY_ITEM_DEFAULT_SIMULATOR_ID = QUuid();
 
 // Certifiable Properties
diff --git a/libraries/entities/src/EntityPropertyFlags.h b/libraries/entities/src/EntityPropertyFlags.h
index 969fd007f1..e86cccb997 100644
--- a/libraries/entities/src/EntityPropertyFlags.h
+++ b/libraries/entities/src/EntityPropertyFlags.h
@@ -26,6 +26,7 @@ enum EntityPropertyList {
     PROP_NAME,
     PROP_LOCKED,
     PROP_USER_DATA,
+    PROP_PRIVATE_USER_DATA,
     PROP_HREF,
     PROP_DESCRIPTION,
     PROP_POSITION,
diff --git a/libraries/entities/src/EntityTree.cpp b/libraries/entities/src/EntityTree.cpp
index b3dd78ae92..806f6189e2 100644
--- a/libraries/entities/src/EntityTree.cpp
+++ b/libraries/entities/src/EntityTree.cpp
@@ -1286,6 +1286,14 @@ void EntityTree::fixupTerseEditLogging(EntityItemProperties& properties, QList<Q
         }
     }
 
+    if (properties.privateUserDataChanged()) {
+        int index = changedProperties.indexOf("privateUserData");
+        if (index >= 0) {
+            QString changeHint = properties.getPrivateUserData();
+            changedProperties[index] = QString("privateUserData:") + changeHint;
+        }
+    }
+
     if (properties.parentJointIndexChanged()) {
         int index = changedProperties.indexOf("parentJointIndex");
         if (index >= 0) {
diff --git a/libraries/networking/src/udt/PacketHeaders.h b/libraries/networking/src/udt/PacketHeaders.h
index 274c34a268..8c97b3ca6a 100644
--- a/libraries/networking/src/udt/PacketHeaders.h
+++ b/libraries/networking/src/udt/PacketHeaders.h
@@ -135,6 +135,7 @@ public:
         AudioSoloRequest,
         BulkAvatarTraitsAck,
         StopInjector,
+        PrivateUserData,
         NUM_PACKET_TYPE
     };