diff --git a/indra/newview/llimprocessing.cpp b/indra/newview/llimprocessing.cpp
index 9746178a62..a5809864bd 100644
--- a/indra/newview/llimprocessing.cpp
+++ b/indra/newview/llimprocessing.cpp
@@ -731,18 +731,22 @@ void LLIMProcessing::processNewMessage(LLUUID from_id,
         haystack.mSenderName = agentName;
         haystack.mOwnerID = from_id;
 
+        bool forbid_chat_replacement = false;
+
         switch (dialog)
         {
         case IM_NOTHING_SPECIAL:        // this is the type for regular IMs
         {
             haystack.mType = OmnifilterEngine::eType::InstantMessage;
+            forbid_chat_replacement = true;
             break;
         }
         case IM_SESSION_SEND:           // this is the type for regular group IMs
-        case IM_SESSION_INVITE:         // this is the type for group IM sessions started by ourselves or conferences
+        case IM_SESSION_INVITE:         // this is the type for new group IM sessions - see LLIMMgr::addMessage()
         case IM_DO_NOT_DISTURB_AUTO_RESPONSE:
         {
             haystack.mType = OmnifilterEngine::eType::GroupChat;
+            forbid_chat_replacement = true;
             break;
         }
         case IM_FROM_TASK:
@@ -810,12 +814,17 @@ void LLIMProcessing::processNewMessage(LLUUID from_id,
         const OmnifilterEngine::Needle* needle = OmnifilterEngine::getInstance()->match(haystack);
         if (needle)
         {
-            if (needle->mChatReplace.empty())
+            if (
+                forbid_chat_replacement             // no text replacement for agent messages to prevent forgery attempts
+                || needle->mChatReplace.empty()     // no replacement defined, just suppress the message
+            )
             {
                 return;
             }
 
-            message = needle->mChatReplace;
+            LLSD args;
+            args["REPLACEMENT"] = needle->mChatReplace;
+            message = LLTrans::getString("OmnifilterReplacement", args);
         }
     }
     // </FS:Zi>
diff --git a/indra/newview/llviewermessage.cpp b/indra/newview/llviewermessage.cpp
index 83631e77d1..9b5d1f626b 100644
--- a/indra/newview/llviewermessage.cpp
+++ b/indra/newview/llviewermessage.cpp
@@ -3300,12 +3300,17 @@ void process_chat_from_simulator(LLMessageSystem *msg, void **user_data)
                         ((LLVOAvatar*)chatter)->stopTyping();
                     }
 
-                    if (needle->mChatReplace.empty())
+                    if (
+                        chat.mSourceType == CHAT_SOURCE_AGENT   // no text replacement for agent chat to prevent forgery attempts
+                        || needle->mChatReplace.empty()         // no replacement defined, just suppress the message
+                    )
                     {
                         return;
                     }
 
-                    chat.mText = needle->mChatReplace;
+                    LLSD args;
+                    args["REPLACEMENT"] = needle->mChatReplace;
+                    chat.mText = LLTrans::getString("OmnifilterReplacement", args);
                 }
 
                 break;
diff --git a/indra/newview/skins/default/xui/en/strings.xml b/indra/newview/skins/default/xui/en/strings.xml
index 2640f72fb5..96cdc3b3b4 100644
--- a/indra/newview/skins/default/xui/en/strings.xml
+++ b/indra/newview/skins/default/xui/en/strings.xml
@@ -2849,6 +2849,8 @@ name="Command_360_Capture_Label">360° Snapshot</string>
   <string name="Command_Beacons_Tooltip">Show beacons</string>
   <string name="Command_Omnifilter_Tooltip">Edit the Omnifilter rules</string>
 
+  <string name="OmnifilterReplacement">Omnifilter Replacement: [REPLACEMENT]</string>
+
   <string name="Toolbar_Bottom_Tooltip">currently in your bottom toolbar</string>
   <string name="Toolbar_Left_Tooltip"  >currently in your left toolbar</string>
   <string name="Toolbar_Right_Tooltip" >currently in your right toolbar</string>