diff --git a/Protest/Protocols/Icmp.cs b/Protest/Protocols/Icmp.cs
index af58c154..5ca38a10 100644
--- a/Protest/Protocols/Icmp.cs
+++ b/Protest/Protocols/Icmp.cs
@@ -180,10 +180,10 @@ private static async Task<string> PingAsync(string hostname, string id, int time
                 (int)IPStatus.DestinationHostUnreachable or
                 (int)IPStatus.DestinationNetworkUnreachable => id + ((char)127).ToString() + "Unreachable",
 
-                (int)IPStatus.Success => id + ((char)127).ToString() + reply.RoundtripTime.ToString(),
+                (int)IPStatus.Success  => id + ((char)127).ToString() + reply.RoundtripTime.ToString(),
                 (int)IPStatus.TimedOut => id + ((char)127).ToString() + "Timed out",
-                11050                 => id + ((char)127).ToString() + "General failure",
-                _                     => id + ((char)127).ToString() + reply.Status.ToString(),
+                11050                  => id + ((char)127).ToString() + "General failure",
+                _                      => id + ((char)127).ToString() + reply.Status.ToString(),
             };
         }
         catch (ArgumentException) {
@@ -224,5 +224,4 @@ private static async Task<string> ArpPingAsync(string name, string id) {
         }
     }
 
-
 }
\ No newline at end of file
diff --git a/Protest/Tasks/LastSeen.cs b/Protest/Tasks/LastSeen.cs
index 25509252..34312de6 100644
--- a/Protest/Tasks/LastSeen.cs
+++ b/Protest/Tasks/LastSeen.cs
@@ -1,13 +1,25 @@
 using System.IO;
+using System.Collections.Concurrent;
 using System.Net.NetworkInformation;
+using System.Threading;
 
 namespace Protest.Tasks {
     internal static class LastSeen {
+
+        private static ConcurrentDictionary<string, object> mutexes = new ConcurrentDictionary<string, object>();
+
         public static void Seen(in string ip) {
+            string filename = $"{Data.DIR_LASTSEEN}\\{ip}.txt";
             try {
-                string filename = $"{Data.DIR_LASTSEEN}\\{ip}.txt";
-                File.WriteAllText(filename, DateTime.Now.ToString(Data.DATETIME_FORMAT_LONG));
-                //File.WriteAllText(filename, DateTime.UtcNow.ToString());
+                if (!mutexes.TryGetValue(ip, out object mutex)) {
+                    mutex = new object();
+                    mutexes[ip] = mutex;
+                }
+
+                lock (mutex) {
+                    File.WriteAllText(filename, DateTime.Now.ToString(Data.DATETIME_FORMAT_LONG));
+                    //File.WriteAllText(filename, DateTime.UtcNow.ToString());
+                }
             }
             catch (Exception ex) {
                 Logger.Error(ex);
@@ -17,17 +29,18 @@ public static void Seen(in string ip) {
         public static string HasBeenSeen(in string[] para, bool recordOnly = false) {
             string ip = null;
             for (int i = 1; i < para.Length; i++) {
-                if (para[i].StartsWith("ip="))
+                if (para[i].StartsWith("ip=")) {
                     ip = para[i][3..];
+                }
             }
+
             return HasBeenSeen(ip, recordOnly);
         }
 
         public static string HasBeenSeen(string ip, bool recordOnly = false) {
-            if (ip is null)
-                return null;
+            if (ip is null) return null;
 
-            if (!recordOnly)
+            if (!recordOnly) {
                 try {
                     using Ping p = new Ping();
                     if (p.Send(ip, 1000).Status == IPStatus.Success) {
@@ -36,12 +49,21 @@ public static string HasBeenSeen(string ip, bool recordOnly = false) {
                     }
                 }
                 catch { }
+            }
 
             string filename = $"{Data.DIR_LASTSEEN}\\{ip}.txt";
 
             try {
-                if (File.Exists(filename))
-                    return File.ReadAllText(filename);
+                if (File.Exists(filename)) {
+                    if (!mutexes.TryGetValue(ip, out object mutex)) {
+                        mutex = new object();
+                        mutexes[ip] = mutex;
+                    }
+
+                    lock (mutex) {
+                        return File.ReadAllText(filename);
+                    }
+                }
             }
             catch { }