diff --git a/.github/workflows/codeql.yml b/.github/workflows/codeql.yml
index e611fff..d2b5bf2 100644
--- a/.github/workflows/codeql.yml
+++ b/.github/workflows/codeql.yml
@@ -4,7 +4,7 @@ on:
   push:
     branches: [ "main", "develop" ]
   pull_request:
-    branches: [ "main", "develop" ]
+    branches: [ "main" ]
   schedule:
     - cron: '34 20 * * 6'
 
diff --git a/.github/workflows/dotnet-desktop.yml b/.github/workflows/dotnet-desktop.yml
index f3de30b..d126be3 100644
--- a/.github/workflows/dotnet-desktop.yml
+++ b/.github/workflows/dotnet-desktop.yml
@@ -4,7 +4,7 @@ on:
   push:
     branches: [ "main", "develop" ]
   pull_request:
-    branches: [ "main", "develop" ]
+    branches: [ "main" ]
 
 jobs:
   build:
diff --git a/HostDownloader/Modules/HostListDownloaderInternals/HostListManager.cs b/HostDownloader/Modules/HostListDownloaderInternals/HostListManager.cs
index 51f5b42..2a744e0 100644
--- a/HostDownloader/Modules/HostListDownloaderInternals/HostListManager.cs
+++ b/HostDownloader/Modules/HostListDownloaderInternals/HostListManager.cs
@@ -26,6 +26,7 @@
 using System.Diagnostics;
 using System.Text.Json;
 using System.Text.RegularExpressions;
+using System.Transactions;
 
 namespace HostlistDownloader.Modules.HostListDownloaderInternals
 {
@@ -76,7 +77,7 @@ public static void StartListProcessing(bool forceMode, CancellationToken cancell
 
                 ProcessDownloadLists(blockListIni,
                     IOManager.BlockListFolderLocation,
-                    IOManager.CombinedBlockListFileLocation, forceMode, cancellationToken).GetAwaiter().GetResult();
+                    IOManager.CombinedBlockListFileLocationTemp, forceMode, cancellationToken).GetAwaiter().GetResult();
             }
             else
             {
@@ -86,7 +87,7 @@ public static void StartListProcessing(bool forceMode, CancellationToken cancell
             if (userblockListIni.Length != 0)
             {
                 TraceLogger.Log("User blocklist is configured. Merging user config...");
-                MergeUserDefinedDomains(IOManager.CombinedBlockListFileLocation, isBlocklist: true);
+                MergeUserDefinedDomains(IOManager.CombinedBlockListFileLocationTemp, isBlocklist: true);
             }
             else
             {
@@ -115,7 +116,7 @@ public static void StartListProcessing(bool forceMode, CancellationToken cancell
                 TraceLogger.Log("Whitelist is configured. Updating whitelists...");
                 ProcessDownloadLists(whiteListIni,
                     IOManager.WhiteListFolderLocation,
-                    IOManager.CombinedWhiteListFileLocation, forceMode, cancellationToken).GetAwaiter().GetResult();
+                    IOManager.CombinedWhiteListFileLocationTemp, forceMode, cancellationToken).GetAwaiter().GetResult();
             }
             else
             {
@@ -125,7 +126,7 @@ public static void StartListProcessing(bool forceMode, CancellationToken cancell
             if (userwhiteListIni.Length != 0)
             {
                 TraceLogger.Log("User Whitelist is configured. Merging user config...");
-                MergeUserDefinedDomains(IOManager.CombinedWhiteListFileLocation, isBlocklist: false);
+                MergeUserDefinedDomains(IOManager.CombinedWhiteListFileLocationTemp, isBlocklist: false);
             }
             else
             {
@@ -136,9 +137,56 @@ public static void StartListProcessing(bool forceMode, CancellationToken cancell
             {
                 GenerateCombinedList();
             }
+            CommitToMasterLists();
 
             TraceLogger.Log("Host lists update completed!");
         }
+        /// <summary>
+        /// Commits the temporary generated hostfile files to the final master version.
+        /// This is done to allow a fallback in the event that something goes wrong, so if the generation fails spectacularly, it wont overwrite the existing master lists with a broken version.
+        /// </summary>
+        private static void CommitToMasterLists()
+        {
+            //Move the temp combined lists to their final locations
+            //e.g. HLDcombined-blocklist-TEMP.txt and HLDcombined-whitelist-TEMP.txt will be moved to HLDcombined-blocklist.txt and HLDcombined-whitelist.txt respectively.
+            //This is done to ensure that the combined lists are only updated if the entire process completes successfully. And also to prevent OS file locks from preventing the combined lists from being updated.
+            TraceLogger.Log("Committing temporary combined lists to final locations...");
+            try
+            {
+                if (File.Exists(IOManager.CombinedBlockListFileLocationTemp))
+                {
+                    File.Move(IOManager.CombinedBlockListFileLocationTemp, IOManager.CombinedBlockListFileLocation, overwrite: true);
+                    TraceLogger.Log($"Committed {IOManager.CombinedBlockListFileLocationTemp} to {IOManager.CombinedBlockListFileLocation}", Enums.StatusSeverityType.Debug);
+                }
+                if (File.Exists(IOManager.CombinedWhiteListFileLocationTemp))
+                {
+                    File.Move(IOManager.CombinedWhiteListFileLocationTemp, IOManager.CombinedWhiteListFileLocation, overwrite: true);
+                    TraceLogger.Log($"Committed {IOManager.CombinedWhiteListFileLocationTemp} to {IOManager.CombinedWhiteListFileLocation}", Enums.StatusSeverityType.Debug);
+                }
+                if (File.Exists(IOManager.CombinedListFileLocationTemp))
+                {
+                    File.Move(IOManager.CombinedListFileLocationTemp, IOManager.CombinedListFileLocation, overwrite: true);
+                    TraceLogger.Log($"Committed {IOManager.CombinedListFileLocationTemp} to {IOManager.CombinedListFileLocation}", Enums.StatusSeverityType.Debug);
+                }
+                string[] FilesToCreate = new string[]
+                {
+                    IOManager.CombinedBlockListFileLocationTemp,
+                    IOManager.CombinedWhiteListFileLocationTemp,
+                    IOManager.CombinedListFileLocationTemp
+                };
+                foreach (string file in FilesToCreate)
+                {
+                    File.Create(file).Dispose();
+                }
+                TraceLogger.Log("Temporary combined lists cleared after committing to final locations.",Enums.StatusSeverityType.Debug);
+            }
+            catch (Exception ex)
+            {
+                ProblemDuringUpdate = true;
+                TraceLogger.Log($"Failed to commit combined lists to final locations: {ex}", Enums.StatusSeverityType.Error);
+                TraceLogger.Log("[!] No changes were made to the final combined lists. Please check the logs for details.", Enums.StatusSeverityType.Error);
+            }
+        }
 
         public static void StartOfflineListProcessing()
         {
@@ -156,7 +204,7 @@ public static void StartOfflineListProcessing()
             if (blockListIni.Length != 0)
             {
                 TraceLogger.Log("Blocklist is configured. Merging...");
-                CompileList(IOManager.BlockListFolderLocation, IOManager.CombinedBlockListFileLocation, blockListIni.Length, 0, DateTime.Now);
+                CompileList(IOManager.BlockListFolderLocation, IOManager.CombinedBlockListFileLocationTemp, blockListIni.Length, 0, DateTime.Now);
             }
             else
             {
@@ -165,7 +213,7 @@ public static void StartOfflineListProcessing()
             if (whiteListIni.Length != 0)
             {
                 TraceLogger.Log("Whitelist is configured. Merging user config...");
-                CompileList(IOManager.WhiteListFolderLocation, IOManager.CombinedWhiteListFileLocation, whiteListIni.Length, 0, DateTime.Now);
+                CompileList(IOManager.WhiteListFolderLocation, IOManager.CombinedWhiteListFileLocationTemp, whiteListIni.Length, 0, DateTime.Now);
             }
             else
             {
@@ -175,7 +223,7 @@ public static void StartOfflineListProcessing()
             if (userwhiteListIni.Length != 0)
             {
                 TraceLogger.Log("User Whitelist is configured. Merging user config...");
-                MergeUserDefinedDomains(IOManager.CombinedWhiteListFileLocation, isBlocklist: false);
+                MergeUserDefinedDomains(IOManager.CombinedWhiteListFileLocationTemp, isBlocklist: false);
             }
             else
             {
@@ -184,7 +232,7 @@ public static void StartOfflineListProcessing()
             if (userblockListIni.Length != 0)
             {
                 TraceLogger.Log("User blocklist is configured. Merging user config...");
-                MergeUserDefinedDomains(IOManager.CombinedBlockListFileLocation, isBlocklist: true);
+                MergeUserDefinedDomains(IOManager.CombinedBlockListFileLocationTemp, isBlocklist: true);
             }
             else
             {
@@ -192,6 +240,7 @@ public static void StartOfflineListProcessing()
             }
 
             GenerateCombinedList();
+            CommitToMasterLists();
         }
 
         /// <summary>
@@ -625,11 +674,11 @@ private static bool CheckIntegrity(string ListFolderLocation, int urlCount, int
 
         public static void GenerateCombinedList()
         {
-            TraceLogger.Log($"Generating {Path.GetFileName(IOManager.CombinedListFileLocation)} list...");
+            TraceLogger.Log($"Generating {Path.GetFileName(IOManager.CombinedListFileLocationTemp)} list...");
             try
             {
-                var whiteList = ReadLinesFromFileCached(IOManager.CombinedWhiteListFileLocation);
-                var blockListLines = ReadLinesFromFile(IOManager.CombinedBlockListFileLocation);
+                var whiteList = ReadLinesFromFileCached(IOManager.CombinedWhiteListFileLocationTemp);
+                var blockListLines = ReadLinesFromFile(IOManager.CombinedBlockListFileLocationTemp);
                 var filteredLines = blockListLines.Where(line =>
                     !whiteList.Any(whiteItem =>
                     {
@@ -641,8 +690,8 @@ public static void GenerateCombinedList()
                         return line.Equals(whiteItem, StringComparison.OrdinalIgnoreCase);
                     })
                 ).ToList();
-                File.WriteAllLines(IOManager.CombinedListFileLocation, filteredLines);
-                TraceLogger.Log($"Generated combined list to: {IOManager.CombinedListFileLocation} | Line count: {filteredLines.Count:N0}");
+                File.WriteAllLines(IOManager.CombinedListFileLocationTemp, filteredLines);
+                TraceLogger.Log($"Generated combined list to: {IOManager.CombinedListFileLocationTemp} | Line count: {filteredLines.Count:N0}");
             }
             catch (Exception ex)
             {
diff --git a/HostDownloader/Modules/WindowsSystem/IOManager.cs b/HostDownloader/Modules/WindowsSystem/IOManager.cs
index cad5d6a..1f9694d 100644
--- a/HostDownloader/Modules/WindowsSystem/IOManager.cs
+++ b/HostDownloader/Modules/WindowsSystem/IOManager.cs
@@ -37,9 +37,19 @@ internal class IOManager
         //public static readonly string IniWhiteListFileLocation = "hostfiles/whitelist.ini";
         //public static readonly string IniUserWebsiteBlockListFileLocation = "hostfiles/userwebsiteblocklist.ini";
         //public static readonly string IniUserWebsiteWhiteListFileLocation = "hostfiles/userwebsitewhitelist.ini";
+        //Note these combined directories are the final saving location, when HostlistManager merges the files, it will save temp files and once the merge is complete, it will move the final merged file to this location. The temp files will be deleted after the merge is complete.
+        //Temp file names will be HLDcombined-*whitelist/blocklist*-TEMP.txt
+        //public static readonly string CombinedBlockListFileLocationTemp = "hostfiles/combined/HLDcombined-blocklist-TEMP.txt";
+        //public static readonly string CombinedWhiteListFileLocationTemp = "hostfiles/combined/HLDcombined-whitelist-TEMP.txt";
+        //public static readonly string CombinedListFileLocationTemp = "hostfiles/combined/HLDcombined-list-TEMP.txt";
+
         public static readonly string CombinedBlockListFileLocation = "hostfiles/combined/HLDcombined-blocklist.txt";
         public static readonly string CombinedWhiteListFileLocation = "hostfiles/combined/HLDcombined-whitelist.txt";
         public static readonly string CombinedListFileLocation = "hostfiles/combined/HLDcombined-list.txt";
+
+        public static readonly string CombinedBlockListFileLocationTemp = "hostfiles/combined/HLDcombined-blocklist-TEMP.txt";
+        public static readonly string CombinedWhiteListFileLocationTemp = "hostfiles/combined/HLDcombined-whitelist-TEMP.txt";
+        public static readonly string CombinedListFileLocationTemp = "hostfiles/combined/HLDcombined-list-TEMP.txt";
         //public static readonly string IniFormatTypeLocation = "hostfiles/formattype.ini";
         public static readonly string LogsLocation = "logs";
         public static readonly string SettingJsonFileLocation = "settings.json";
@@ -65,7 +75,7 @@ public static void CreateNecessaryDirectoriesAndFiles()
                     }
                 }
             }
-            string[] files = [CombinedListFileLocation, CombinedBlockListFileLocation, CombinedWhiteListFileLocation];
+            string[] files = [CombinedListFileLocationTemp, CombinedBlockListFileLocationTemp, CombinedWhiteListFileLocationTemp];
             foreach (string file in files)
             {
                 if (!File.Exists(file))
@@ -77,7 +87,7 @@ public static void CreateNecessaryDirectoriesAndFiles()
                         if (!string.IsNullOrEmpty(directory) && !Directory.Exists(directory))
                             Directory.CreateDirectory(directory);
                         File.Create(file).Dispose();
-                        TraceLogger.Log($"Created file: {file}");
+                        TraceLogger.Log($"Created file: {file}", Enums.StatusSeverityType.Debug);
                     }
                     catch (Exception ex)
                     {