diff --git a/res/layout/appdetails.xml b/res/layout/appdetails.xml
index 057645189..ee88f8e19 100644
--- a/res/layout/appdetails.xml
+++ b/res/layout/appdetails.xml
@@ -28,6 +28,10 @@
 				android:textSize="12sp" android:layout_height="wrap_content"
 				android:layout_width="fill_parent" />
 
+			<TextView android:id="@+id/signature" android:layout_below="@id/status"
+				android:layout_alignParentLeft="true" android:textSize="12sp"
+				android:layout_height="wrap_content" android:layout_width="fill_parent" />
+
 		</RelativeLayout>
 
 	</LinearLayout>
diff --git a/res/values/strings.xml b/res/values/strings.xml
index ddc4145c6..4afc6faec 100644
--- a/res/values/strings.xml
+++ b/res/values/strings.xml
@@ -115,4 +115,7 @@
 	<string name="antinonfreenet">Network Services</string>
 	<string name="antinonfreenetlong">Show apps that promote non-free network services</string>
 
+	<string name="expert">Expert</string>
+	<string name="expert_mode">Enabled expert mode</string>
+
 </resources>
diff --git a/res/xml/preferences.xml b/res/xml/preferences.xml
index 7baff4fe6..6ad6b66fb 100644
--- a/res/xml/preferences.xml
+++ b/res/xml/preferences.xml
@@ -7,9 +7,9 @@
 	</PreferenceCategory>
 	<PreferenceCategory android:title="@string/updates">
 		<ListPreference android:title="@string/automatic_repo_scan"
-			android:summary="@string/update_apps_list"
-			android:key="updateInterval" android:defaultValue="0"
-			android:entries="@array/updateIntervalNames" android:entryValues="@array/updateIntervalValues" />
+			android:summary="@string/update_apps_list" android:key="updateInterval"
+			android:defaultValue="0" android:entries="@array/updateIntervalNames"
+			android:entryValues="@array/updateIntervalValues" />
 		<CheckBoxPreference android:title="@string/notify"
 			android:defaultValue="false" android:summary="@string/notify_updates_available"
 			android:key="updateNotify" />
@@ -29,9 +29,10 @@
 			android:key="cacheDownloaded" />
 	</PreferenceCategory>
 	<PreferenceCategory android:title="@string/maintenance">
-	        <Preference
-                android:title="@string/reset"
-                android:summary="@string/clear_all_cached_data"
-                android:key="reset" />
-	</PreferenceCategory>	
+		<Preference android:title="@string/reset" android:summary="@string/clear_all_cached_data"
+			android:key="reset" />
+		<CheckBoxPreference android:title="@string/expert"
+			android:defaultValue="false" android:summary="@string/expert_mode"
+			android:key="expert" />
+	</PreferenceCategory>
 </PreferenceScreen>
diff --git a/src/org/fdroid/fdroid/AppDetails.java b/src/org/fdroid/fdroid/AppDetails.java
index 551e02320..f0cb9a332 100644
--- a/src/org/fdroid/fdroid/AppDetails.java
+++ b/src/org/fdroid/fdroid/AppDetails.java
@@ -22,7 +22,10 @@ import java.io.BufferedInputStream;
 import java.io.BufferedOutputStream;
 import java.io.File;
 import java.io.FileOutputStream;
+import java.math.BigInteger;
 import java.net.URL;
+import java.security.MessageDigest;
+import java.security.NoSuchAlgorithmException;
 import java.util.ArrayList;
 import java.util.List;
 
@@ -43,6 +46,7 @@ import android.widget.TextView;
 import android.widget.Toast;
 import android.content.pm.PackageManager;
 import android.content.pm.PackageInfo;
+import android.content.pm.Signature;
 import android.content.pm.PackageManager.NameNotFoundException;
 import android.content.Context;
 import android.content.DialogInterface;
@@ -162,8 +166,12 @@ public class AppDetails extends ListActivity {
     }
 
     private boolean pref_cacheDownloaded;
+    private boolean pref_expert;
     private boolean viewResetRequired;
 
+    // The signature of the installed version.
+    private Signature mInstalledSignature;
+
     @Override
     protected void onStart() {
         super.onStart();
@@ -174,6 +182,7 @@ public class AppDetails extends ListActivity {
         SharedPreferences prefs = PreferenceManager
                 .getDefaultSharedPreferences(getBaseContext());
         pref_cacheDownloaded = prefs.getBoolean("cacheDownloaded", true);
+        pref_expert = prefs.getBoolean("expert", false);
         viewResetRequired = true;
 
     }
@@ -204,6 +213,19 @@ public class AppDetails extends ListActivity {
         DB.Apk curver = app.getCurrentVersion();
         app_currentvercode = curver == null ? 0 : curver.vercode;
 
+        // Get the signature of the installed package...
+        mInstalledSignature = null;
+        if (curver != null) {
+            PackageManager pm = getBaseContext().getPackageManager();
+            try {
+                PackageInfo pi = pm.getPackageInfo(appid,
+                        PackageManager.GET_SIGNATURES);
+                mInstalledSignature = pi.signatures[0];
+            } catch (NameNotFoundException e) {
+                Log.d("FDroid", "Failed to get installed signature");
+            }
+        }
+
         // Set the icon...
         ImageView iv = (ImageView) findViewById(R.id.icon);
         String icon_path = DB.getIconsPath() + app.icon;
@@ -229,6 +251,23 @@ public class AppDetails extends ListActivity {
                     app.installedVersion));
         tv = (TextView) findViewById(R.id.description);
         tv.setText(app.description);
+        if (pref_expert && mInstalledSignature != null) {
+            try {
+                tv = (TextView) findViewById(R.id.signature);
+                byte[] sig = mInstalledSignature.toByteArray();
+                MessageDigest md;
+                md = MessageDigest.getInstance("MD5");
+                byte[] md5sum = new byte[32];
+                md.update(sig, 0, sig.length);
+                md5sum = md.digest();
+                BigInteger bigInt = new BigInteger(1, md5sum);
+                String md5hash = bigInt.toString(16);
+                while (md5hash.length() < 32)
+                    md5hash = "0" + md5hash;
+                tv.setText("Signed: " + md5hash);
+            } catch (NoSuchAlgorithmException e) {
+            }
+        }
 
         // Set up the list...
         ApkListAdapter la = new ApkListAdapter(this);