diff --git a/shadowsocks-csharp/Controller/Service/PACServer.cs b/shadowsocks-csharp/Controller/Service/PACServer.cs
index d5813f0d9..9a9af528d 100644
--- a/shadowsocks-csharp/Controller/Service/PACServer.cs
+++ b/shadowsocks-csharp/Controller/Service/PACServer.cs
@@ -10,6 +10,7 @@
 using Shadowsocks.Properties;
 using Shadowsocks.Util;
 using System.Threading.Tasks;
+using System.Web;
 
 namespace Shadowsocks.Controller
 {
@@ -17,8 +18,20 @@ public class PACServer : Listener.Service
     {
         public const string RESOURCE_NAME = "pac";
 
-        private string PacSecret { get; set; } = "";
-
+        private string PacSecret
+        {
+            get
+            {
+                if (string.IsNullOrEmpty(_cachedPacSecret))
+                {
+                    var rd = new byte[32];
+                    RNG.GetBytes(rd);
+                    _cachedPacSecret = HttpServerUtility.UrlTokenEncode(rd);
+                }
+                return _cachedPacSecret;
+            }
+        }
+        private string _cachedPacSecret = "";
         public string PacUrl { get; private set; } = "";
 
         private Configuration _config;
@@ -31,26 +44,21 @@ public PACServer(PACDaemon pacDaemon)
 
         public void UpdatePACURL(Configuration config)
         {
-            this._config = config;
-
-            if (config.secureLocalPac)
-            {
-                var rd = new byte[32];
-                RNG.GetBytes(rd);
-                PacSecret = $"&secret={Convert.ToBase64String(rd)}";
-            }
-            else
-            {
-                PacSecret = "";
-            }
-
-            PacUrl = $"http://{config.localHost}:{config.localPort}/{RESOURCE_NAME}?t={GetTimestamp(DateTime.Now)}{PacSecret}";
+            _config = config;
+            string usedSecret = _config.secureLocalPac ? $"&secret={PacSecret}" : "";
+            string contentHash = GetHash(_pacDaemon.GetPACContent());
+            PacUrl = $"http://{config.localHost}:{config.localPort}/{RESOURCE_NAME}?hash={contentHash}{usedSecret}";
+            Logging.Debug("Set PAC URL:" + PacUrl);
         }
 
-
-        private static string GetTimestamp(DateTime value)
+        private static string GetHash(string content)
         {
-            return value.ToString("yyyyMMddHHmmssfff");
+            var contentBytes = Encoding.ASCII.GetBytes(content);
+            using (var md5 = System.Security.Cryptography.MD5.Create())
+            {
+                var md5Bytes = md5.ComputeHash(contentBytes);
+                return HttpServerUtility.UrlTokenEncode(md5Bytes);
+            };
         }
 
         public override bool Handle(byte[] firstPacket, int length, Socket socket, object state)
@@ -74,7 +82,7 @@ public override bool Handle(byte[] firstPacket, int length, Socket socket, objec
                 string request = Encoding.UTF8.GetString(firstPacket, 0, length);
                 string[] lines = request.Split('\r', '\n');
                 bool hostMatch = false, pathMatch = false, useSocks = false;
-                bool secretMatch = PacSecret.IsNullOrEmpty();
+                bool secretMatch = _config.secureLocalPac;
 
                 if (lines.Length < 2)   // need at lease RequestLine + Host
                 {
@@ -165,7 +173,7 @@ public void SendResponse(Socket socket, bool useSocks)
                 string proxy = GetPACAddress(localEndPoint, useSocks);
 
                 string pacContent = $"var __PROXY__ = '{proxy}';\n" + _pacDaemon.GetPACContent();
-                string responseHead = 
+                string responseHead =
 $@"HTTP/1.1 200 OK
 Server: ShadowsocksWindows/{UpdateChecker.Version}
 Content-Type: application/x-ns-proxy-autoconfig
diff --git a/shadowsocks-csharp/Controller/ShadowsocksController.cs b/shadowsocks-csharp/Controller/ShadowsocksController.cs
index 0056e20b8..79ff929d1 100644
--- a/shadowsocks-csharp/Controller/ShadowsocksController.cs
+++ b/shadowsocks-csharp/Controller/ShadowsocksController.cs
@@ -465,38 +465,19 @@ protected void Reload()
             _config = Configuration.Load();
             StatisticsConfiguration = StatisticsStrategyConfiguration.Load();
 
-            if (privoxyRunner == null)
-            {
-                privoxyRunner = new PrivoxyRunner();
-            }
+            privoxyRunner = privoxyRunner ?? new PrivoxyRunner();
 
-            if (_pacDaemon == null)
-            {
-                _pacDaemon = new PACDaemon();
-                _pacDaemon.PACFileChanged += PacDaemon_PACFileChanged;
-                _pacDaemon.UserRuleFileChanged += PacDaemon_UserRuleFileChanged;
-            }
+            _pacDaemon = _pacDaemon ?? new PACDaemon();
+            _pacDaemon.PACFileChanged += PacDaemon_PACFileChanged;
+            _pacDaemon.UserRuleFileChanged += PacDaemon_UserRuleFileChanged;
+            _pacServer = _pacServer ?? new PACServer(_pacDaemon);
 
-            if (_pacServer == null)
-            {
-                _pacServer = new PACServer(_pacDaemon);
-            }
-
-            _pacServer.UpdatePACURL(_config);
-            if (gfwListUpdater == null)
-            {
-                gfwListUpdater = new GFWListUpdater();
-                gfwListUpdater.UpdateCompleted += PacServer_PACUpdateCompleted;
-                gfwListUpdater.Error += PacServer_PACUpdateError;
-            }
+            gfwListUpdater = gfwListUpdater ?? new GFWListUpdater();
+            gfwListUpdater.UpdateCompleted += PacServer_PACUpdateCompleted;
+            gfwListUpdater.Error += PacServer_PACUpdateError;
 
             availabilityStatistics.UpdateConfiguration(this);
-
-            if (_listener != null)
-            {
-                _listener.Stop();
-            }
-
+            _listener?.Stop();
             StopPlugins();
 
             // don't put PrivoxyRunner.Start() before pacServer.Stop()
@@ -507,10 +488,7 @@ protected void Reload()
             try
             {
                 var strategy = GetCurrentStrategy();
-                if (strategy != null)
-                {
-                    strategy.ReloadServers();
-                }
+                strategy?.ReloadServers();
 
                 StartPlugin();
                 privoxyRunner.Start(_config);
@@ -547,7 +525,6 @@ protected void Reload()
             }
 
             ConfigChanged?.Invoke(this, new EventArgs());
-
             UpdateSystemProxy();
             Utils.ReleaseMemory(true);
         }
diff --git a/shadowsocks-csharp/Controller/System/SystemProxy.cs b/shadowsocks-csharp/Controller/System/SystemProxy.cs
index f02d3d115..e11342abb 100644
--- a/shadowsocks-csharp/Controller/System/SystemProxy.cs
+++ b/shadowsocks-csharp/Controller/System/SystemProxy.cs
@@ -39,6 +39,7 @@ public static void Update(Configuration config, bool forceDisable, PACServer pac
                         }
                         else
                         {
+                            pacSrv.UpdatePACURL(config);
                             pacUrl = pacSrv.PacUrl;
                         }
                         Sysproxy.SetIEProxy(true, false, null, pacUrl);