diff --git a/shadowsocks-csharp/Controller/Service/GfwListUpdater.cs b/shadowsocks-csharp/Controller/Service/GfwListUpdater.cs
index d59fcec..702170d 100644
--- a/shadowsocks-csharp/Controller/Service/GfwListUpdater.cs
+++ b/shadowsocks-csharp/Controller/Service/GfwListUpdater.cs
@@ -36,42 +36,8 @@ namespace Shadowsocks.Controller
             try
             {
                 File.WriteAllText(Utils.GetTempPath("gfwlist.txt"), e.Result, Encoding.UTF8);
-                List<string> lines = new List<string>();
-                if (File.Exists(PACServer.USER_RULE_FILE))
-                {
-                    string local = FileManager.NonExclusiveReadAllText(PACServer.USER_RULE_FILE, Encoding.UTF8);
-                    using (var sr = new StringReader(local))
-                    {
-                        foreach (var rule in sr.NonWhiteSpaceLines())
-                        {
-                            if (rule.BeginWithAny(IgnoredLineBegins))
-                                continue;
-                            lines.Add(rule);
-                        }
-                    }
-                }
-                lines.AddRange(ParseResult(e.Result));
-                string abpContent;
-                if (File.Exists(PACServer.USER_ABP_FILE))
-                {
-                    abpContent = FileManager.NonExclusiveReadAllText(PACServer.USER_ABP_FILE, Encoding.UTF8);
-                }
-                else
-                {
-                    abpContent = Utils.UnGzip(Resources.abp_js);
-                }
-                abpContent = abpContent.Replace("__RULES__", JsonConvert.SerializeObject(lines, Formatting.Indented));
-                if (File.Exists(PACServer.PAC_FILE))
-                {
-                    string original = FileManager.NonExclusiveReadAllText(PACServer.PAC_FILE, Encoding.UTF8);
-                    if (original == abpContent)
-                    {
-                        UpdateCompleted(this, new ResultEventArgs(false));
-                        return;
-                    }
-                }
-                File.WriteAllText(PACServer.PAC_FILE, abpContent, Encoding.UTF8);
-                UpdateCompleted?.Invoke(this, new ResultEventArgs(true));
+                bool pacFileChanged = MergeAndWritePACFile(e.Result);
+                UpdateCompleted?.Invoke(this, new ResultEventArgs(pacFileChanged));
             }
             catch (Exception ex)
             {
@@ -79,6 +45,45 @@ namespace Shadowsocks.Controller
             }
         }
 
+        public static bool MergeAndWritePACFile(string gfwListResult)
+        {
+            List<string> lines = new List<string>();
+            if (File.Exists(PACServer.USER_RULE_FILE))
+            {
+                string local = FileManager.NonExclusiveReadAllText(PACServer.USER_RULE_FILE, Encoding.UTF8);
+                using (var sr = new StringReader(local))
+                {
+                    foreach (var rule in sr.NonWhiteSpaceLines())
+                    {
+                        if (rule.BeginWithAny(IgnoredLineBegins))
+                            continue;
+                        lines.Add(rule);
+                    }
+                }
+            }
+            lines.AddRange(ParseResult(gfwListResult));
+            string abpContent;
+            if (File.Exists(PACServer.USER_ABP_FILE))
+            {
+                abpContent = FileManager.NonExclusiveReadAllText(PACServer.USER_ABP_FILE, Encoding.UTF8);
+            }
+            else
+            {
+                abpContent = Utils.UnGzip(Resources.abp_js);
+            }
+            abpContent = abpContent.Replace("__RULES__", JsonConvert.SerializeObject(lines, Formatting.Indented));
+            if (File.Exists(PACServer.PAC_FILE))
+            {
+                string original = FileManager.NonExclusiveReadAllText(PACServer.PAC_FILE, Encoding.UTF8);
+                if (original == abpContent)
+                {
+                    return false;
+                }
+            }
+            File.WriteAllText(PACServer.PAC_FILE, abpContent, Encoding.UTF8);
+            return true;
+        }
+
         public void UpdatePACFromGFWList(Configuration config)
         {
             WebClient http = new WebClient();
diff --git a/shadowsocks-csharp/Controller/ShadowsocksController.cs b/shadowsocks-csharp/Controller/ShadowsocksController.cs
index 89d4351..8f2fd01 100644
--- a/shadowsocks-csharp/Controller/ShadowsocksController.cs
+++ b/shadowsocks-csharp/Controller/ShadowsocksController.cs
@@ -612,46 +612,14 @@ namespace Shadowsocks.Controller
         private static readonly IEnumerable<char> IgnoredLineBegins = new[] { '!', '[' };
         private void pacServer_UserRuleFileChanged(object sender, EventArgs e)
         {
-            // TODO: this is a dirty hack. (from code GListUpdater.http_DownloadStringCompleted())
             if (!File.Exists(Utils.GetTempPath("gfwlist.txt")))
             {
                 UpdatePACFromGFWList();
-                return;
-            }
-            List<string> lines = new List<string>();
-            if (File.Exists(PACServer.USER_RULE_FILE))
-            {
-                string local = FileManager.NonExclusiveReadAllText(PACServer.USER_RULE_FILE, Encoding.UTF8);
-                using (var sr = new StringReader(local))
-                {
-                    foreach (var rule in sr.NonWhiteSpaceLines())
-                    {
-                        if (rule.BeginWithAny(IgnoredLineBegins))
-                            continue;
-                        lines.Add(rule);
-                    }
-                }
-            }
-            lines.AddRange(GFWListUpdater.ParseResult(FileManager.NonExclusiveReadAllText(Utils.GetTempPath("gfwlist.txt"))));
-            string abpContent;
-            if (File.Exists(PACServer.USER_ABP_FILE))
-            {
-                abpContent = FileManager.NonExclusiveReadAllText(PACServer.USER_ABP_FILE, Encoding.UTF8);
             }
             else
             {
-                abpContent = Utils.UnGzip(Resources.abp_js);
+                GFWListUpdater.MergeAndWritePACFile(FileManager.NonExclusiveReadAllText(Utils.GetTempPath("gfwlist.txt")));
             }
-            abpContent = abpContent.Replace("__RULES__", JsonConvert.SerializeObject(lines, Formatting.Indented));
-            if (File.Exists(PACServer.PAC_FILE))
-            {
-                string original = FileManager.NonExclusiveReadAllText(PACServer.PAC_FILE, Encoding.UTF8);
-                if (original == abpContent)
-                {
-                    return;
-                }
-            }
-            File.WriteAllText(PACServer.PAC_FILE, abpContent, Encoding.UTF8);
         }
 
         public void CopyPacUrl()