diff --git a/app/src/main/java/com/github/kr328/clash/FeedbackActivity.kt b/app/src/main/java/com/github/kr328/clash/FeedbackActivity.kt
index f23d1e1..5f8ab06 100644
--- a/app/src/main/java/com/github/kr328/clash/FeedbackActivity.kt
+++ b/app/src/main/java/com/github/kr328/clash/FeedbackActivity.kt
@@ -1,15 +1,37 @@
 package com.github.kr328.clash
 
+import android.content.ClipData
+import android.content.ClipboardManager
 import android.os.Bundle
+import android.widget.Toast
 import androidx.annotation.Keep
+import androidx.preference.Preference
 import androidx.preference.PreferenceFragmentCompat
 import kotlinx.android.synthetic.main.activity_feedback.*
 
 class FeedbackActivity : BaseActivity() {
+    companion object {
+        const val KEY_FEEDBACK_ID = "feedback_id"
+    }
+
     @Keep
     class Fragment : PreferenceFragmentCompat() {
         override fun onCreatePreferences(savedInstanceState: Bundle?, rootKey: String?) {
             setPreferencesFromResource(R.xml.feedback, rootKey)
+
+            findPreference<Preference>(KEY_FEEDBACK_ID)?.apply {
+                summary = MainApplication.userIdentifier
+
+                onPreferenceClickListener = Preference.OnPreferenceClickListener { p ->
+                    val data = ClipData.newPlainText("userIdentifier", summary)
+
+                    requireContext().getSystemService(ClipboardManager::class.java)?.setPrimaryClip(data)
+
+                    Toast.makeText(requireContext(), R.string.feedback_feedback_id_copied, Toast.LENGTH_LONG).show()
+
+                    true
+                }
+            }
         }
     }
 
diff --git a/app/src/main/java/com/github/kr328/clash/MainApplication.kt b/app/src/main/java/com/github/kr328/clash/MainApplication.kt
index 9561e2f..6bbb678 100644
--- a/app/src/main/java/com/github/kr328/clash/MainApplication.kt
+++ b/app/src/main/java/com/github/kr328/clash/MainApplication.kt
@@ -2,11 +2,14 @@ package com.github.kr328.clash
 
 import android.app.Application
 import android.content.Context
+import android.os.Build
 import com.crashlytics.android.Crashlytics
 import com.github.kr328.clash.core.Constants
 import com.github.kr328.clash.core.utils.Log
 import com.google.firebase.FirebaseApp
 import io.fabric.sdk.android.Fabric
+import java.security.MessageDigest
+import kotlin.experimental.and
 
 
 class MainApplication : Application() {
@@ -16,10 +19,28 @@ class MainApplication : Application() {
         const val PROXY_MODE_PROXY_ONLY = "proxy_only"
 
         val GOOGLE_PLAY_INSTALLER = listOf("com.android.vending", "com.google.android.feedback")
-        const val CRASHLYTICS_GOOGLE_PLAY_KEY = "install_from_google"
+        const val CRASHLYTICS_FROM_PLAY_KEY = "install_from_google"
         const val CRASHLYTICS_SPLIT_APK_KEY = "split_apk"
 
+        val userIdentifier: String by lazy {
+            val archive = instance.packageManager.getPackageInfo(instance.packageName, 0)
+            val encoder = MessageDigest.getInstance("md5")
+
+            encoder.digest((Build.ID + archive.lastUpdateTime).toByteArray()).toHexString()
+        }
+
         lateinit var instance: MainApplication
+
+        private fun ByteArray.toHexString(): String {
+            return this.map {
+                Integer.toHexString(it.toInt() and 0xff)
+            }.map {
+                if ( it.length < 2 )
+                    "0$it"
+                else
+                    it
+            }.joinToString(separator = "")
+        }
     }
 
     override fun attachBaseContext(base: Context?) {
@@ -38,8 +59,9 @@ class MainApplication : Application() {
             Fabric.with(this, Crashlytics())
         }
 
-        Crashlytics.setBool(CRASHLYTICS_GOOGLE_PLAY_KEY, detectFromPlay())
+        Crashlytics.setBool(CRASHLYTICS_FROM_PLAY_KEY, detectFromPlay())
         Crashlytics.setBool(CRASHLYTICS_SPLIT_APK_KEY, detectSplitArchive())
+        Crashlytics.setUserIdentifier(userIdentifier)
 
         Log.handler = object: Log.LogHandler {
             override fun info(message: String, throwable: Throwable?) {
diff --git a/app/src/main/res/values/strings.xml b/app/src/main/res/values/strings.xml
index 0e78064..63624bb 100644
--- a/app/src/main/res/values/strings.xml
+++ b/app/src/main/res/values/strings.xml
@@ -94,6 +94,11 @@
     
     <string name="not_implemented">Not Implemented</string>
 
+    <string name="feedback_id">ID</string>
+    <string name="feedback_feedback_id">Feedback ID</string>
+    <string name="feedback_feedback_id_summary">Unknown</string>
+    <string name="feedback_feedback_id_copied">Copied</string>
+
     <string name="feedback_source">Source &amp; Issues</string>
     <string name="feedback_upstream">Upstream</string>
     <string name="feedback_github_repo">Github</string>
diff --git a/app/src/main/res/xml-zh/feedback.xml b/app/src/main/res/xml-zh/feedback.xml
index 8a0d439..78428e9 100644
--- a/app/src/main/res/xml-zh/feedback.xml
+++ b/app/src/main/res/xml-zh/feedback.xml
@@ -1,5 +1,10 @@
 <?xml version="1.0" encoding="utf-8"?>
 <PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android">
+    <PreferenceCategory android:title="@string/feedback_id">
+        <Preference android:title="@string/feedback_feedback_id"
+            android:key="feedback_id"
+            android:summary="@string/feedback_feedback_id_summary" />
+    </PreferenceCategory>
     <PreferenceCategory android:title="@string/feedback_source">
         <Preference android:title="@string/feedback_upstream"
             android:summary="@string/feedback_upstream_url">
diff --git a/app/src/main/res/xml/feedback.xml b/app/src/main/res/xml/feedback.xml
index b76a61b..8e4ba50 100644
--- a/app/src/main/res/xml/feedback.xml
+++ b/app/src/main/res/xml/feedback.xml
@@ -1,5 +1,10 @@
 <?xml version="1.0" encoding="utf-8"?>
 <PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android">
+    <PreferenceCategory android:title="@string/feedback_id">
+        <Preference android:title="@string/feedback_feedback_id"
+            android:key="feedback_id"
+            android:summary="@string/feedback_feedback_id_summary" />
+    </PreferenceCategory>
     <PreferenceCategory android:title="@string/feedback_source">
         <Preference android:title="@string/feedback_upstream"
             android:summary="@string/feedback_upstream_url">