diff --git a/OpenPGP-Keychain/res/layout/api_app_error_message.xml b/OpenPGP-Keychain/res/layout/api_app_error_message.xml
new file mode 100644
index 000000000..5927dbf43
--- /dev/null
+++ b/OpenPGP-Keychain/res/layout/api_app_error_message.xml
@@ -0,0 +1,17 @@
+<?xml version="1.0" encoding="utf-8"?>
+<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
+    xmlns:tools="http://schemas.android.com/tools"
+    android:layout_width="fill_parent"
+    android:layout_height="fill_parent"
+    android:orientation="vertical" >
+
+    <org.sufficientlysecure.htmltextview.HtmlTextView
+        android:id="@+id/api_app_error_message_text"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:padding="8dp"
+        android:paddingBottom="0dip"
+        android:text="Set in-code!"
+        android:textAppearance="?android:attr/textAppearanceLarge" />
+
+</LinearLayout>
\ No newline at end of file
diff --git a/OpenPGP-Keychain/res/values/strings.xml b/OpenPGP-Keychain/res/values/strings.xml
index da82e7553..807daaeb4 100644
--- a/OpenPGP-Keychain/res/values/strings.xml
+++ b/OpenPGP-Keychain/res/values/strings.xml
@@ -338,6 +338,7 @@
     <string name="api_select_pub_keys_missing_text">No public keys were found for these user ids:</string>
     <string name="api_select_pub_keys_dublicates_text">More than one public key exist for these user ids:</string>
     <string name="api_select_pub_keys_text">Please review the list of recipients!</string>
+    <string name="api_error_wrong_signature">Signature check failed! Have you installed this app from a different source? If you are sure that this is not an attack, revoke this app\'s registration in OpenPGP Keychain and then register the app again.</string>
 
     <!-- Share -->
     <string name="share_qr_code_dialog_start">Go through all QR Codes using \'Next\', and scan them one by one.</string>
diff --git a/OpenPGP-Keychain/src/org/sufficientlysecure/keychain/helper/ActionBarHelper.java b/OpenPGP-Keychain/src/org/sufficientlysecure/keychain/helper/ActionBarHelper.java
index c0fc4df86..dcac2df08 100644
--- a/OpenPGP-Keychain/src/org/sufficientlysecure/keychain/helper/ActionBarHelper.java
+++ b/OpenPGP-Keychain/src/org/sufficientlysecure/keychain/helper/ActionBarHelper.java
@@ -102,8 +102,7 @@ public class ActionBarHelper {
         final View customActionBarView = inflater
                 .inflate(R.layout.actionbar_custom_view_done, null);
 
-        ((TextView) customActionBarView.findViewById(R.id.actionbar_done_text))
-                .setText(R.string.api_settings_save);
+        ((TextView) customActionBarView.findViewById(R.id.actionbar_done_text)).setText(doneText);
         customActionBarView.findViewById(R.id.actionbar_done).setOnClickListener(
                 doneOnClickListener);
 
diff --git a/OpenPGP-Keychain/src/org/sufficientlysecure/keychain/service/remote/RemoteService.java b/OpenPGP-Keychain/src/org/sufficientlysecure/keychain/service/remote/RemoteService.java
index 0f28d96f6..bc513d532 100644
--- a/OpenPGP-Keychain/src/org/sufficientlysecure/keychain/service/remote/RemoteService.java
+++ b/OpenPGP-Keychain/src/org/sufficientlysecure/keychain/service/remote/RemoteService.java
@@ -23,6 +23,7 @@ import java.util.concurrent.ArrayBlockingQueue;
 import java.util.concurrent.TimeUnit;
 
 import org.sufficientlysecure.keychain.Constants;
+import org.sufficientlysecure.keychain.R;
 import org.sufficientlysecure.keychain.provider.KeychainContract;
 import org.sufficientlysecure.keychain.provider.ProviderHelper;
 import org.sufficientlysecure.keychain.service.exception.WrongPackageSignatureException;
@@ -140,8 +141,12 @@ public abstract class RemoteService extends Service {
                 }
             }
         } catch (WrongPackageSignatureException e) {
-            // TODO: Inform user about wrong signature!
-            Log.e(Constants.TAG, "RemoteService", e);
+            Log.e(Constants.TAG, e.getMessage());
+
+            Bundle extras = new Bundle();
+            extras.putString(RemoteServiceActivity.EXTRA_ERROR_MESSAGE,
+                    getString(R.string.api_error_wrong_signature));
+            pauseAndStartUserInteraction(RemoteServiceActivity.ACTION_ERROR_MESSAGE, null, extras);
         }
     }
 
@@ -243,8 +248,13 @@ public abstract class RemoteService extends Service {
                         mThreadPool.shutdownNow();
                     }
                 } catch (WrongPackageSignatureException e) {
-                    // TODO: Inform user about wrong signature!
-                    Log.e(Constants.TAG, "RemoteService", e);
+                    Log.e(Constants.TAG, e.getMessage());
+
+                    Bundle extras = new Bundle();
+                    extras.putString(RemoteServiceActivity.EXTRA_ERROR_MESSAGE,
+                            getString(R.string.api_error_wrong_signature));
+                    pauseAndStartUserInteraction(RemoteServiceActivity.ACTION_ERROR_MESSAGE, null,
+                            extras);
                 }
             } else {
                 allowed = false;
diff --git a/OpenPGP-Keychain/src/org/sufficientlysecure/keychain/service/remote/RemoteServiceActivity.java b/OpenPGP-Keychain/src/org/sufficientlysecure/keychain/service/remote/RemoteServiceActivity.java
index bba8176b1..de07989d8 100644
--- a/OpenPGP-Keychain/src/org/sufficientlysecure/keychain/service/remote/RemoteServiceActivity.java
+++ b/OpenPGP-Keychain/src/org/sufficientlysecure/keychain/service/remote/RemoteServiceActivity.java
@@ -48,6 +48,8 @@ public class RemoteServiceActivity extends SherlockFragmentActivity {
             + "API_ACTIVITY_CACHE_PASSPHRASE";
     public static final String ACTION_SELECT_PUB_KEYS = Constants.INTENT_PREFIX
             + "API_ACTIVITY_SELECT_PUB_KEYS";
+    public static final String ACTION_ERROR_MESSAGE = Constants.INTENT_PREFIX
+            + "API_ACTIVITY_ERROR_MESSAGE";
 
     public static final String EXTRA_MESSENGER = "messenger";
 
@@ -60,6 +62,8 @@ public class RemoteServiceActivity extends SherlockFragmentActivity {
     public static final String EXTRA_SELECTED_MASTER_KEY_IDS = "master_key_ids";
     public static final String EXTRA_MISSING_USER_IDS = "missing_user_ids";
     public static final String EXTRA_DUBLICATE_USER_IDS = "dublicate_user_ids";
+    // error message
+    public static final String EXTRA_ERROR_MESSAGE = "error_message";
 
     private Messenger mMessenger;
 
@@ -271,6 +275,27 @@ public class RemoteServiceActivity extends SherlockFragmentActivity {
                 getSupportFragmentManager().beginTransaction()
                         .add(R.id.api_select_pub_keys_fragment_container, mSelectFragment).commit();
             }
+        } else if (ACTION_ERROR_MESSAGE.equals(action)) {
+            String errorMessage = intent.getStringExtra(EXTRA_ERROR_MESSAGE);
+
+            String text = new String();
+            text += "<font color=\"red\">" + errorMessage + "</font>";
+
+            // Inflate a "Done" custom action bar view
+            ActionBarHelper.setDoneView(getSupportActionBar(), R.string.btn_okay,
+                    new View.OnClickListener() {
+
+                        @Override
+                        public void onClick(View v) {
+                            finish();
+                        }
+                    });
+
+            setContentView(R.layout.api_app_error_message);
+
+            // set text on view
+            HtmlTextView textView = (HtmlTextView) findViewById(R.id.api_app_error_message_text);
+            textView.setHtmlFromString(text);
         } else {
             Log.e(Constants.TAG, "Wrong action!");
             finish();