diff --git a/02_Windows_App/Perun_v1/01_Classes/NativeMethods.cs b/02_Windows_App/Perun_v1/01_Classes/NativeMethods.cs
new file mode 100644
index 0000000..4372f27
--- /dev/null
+++ b/02_Windows_App/Perun_v1/01_Classes/NativeMethods.cs
@@ -0,0 +1,13 @@
+// this class just wraps some Win32 stuff that we're going to use for blocking of multiple instances
+using System;
+using System.Runtime.InteropServices;
+
+internal class NativeMethods
+{
+    public const int HWND_BROADCAST = 0xffff;
+    public static readonly int WM_SHOWME = RegisterWindowMessage("WM_SHOWME");
+    [DllImport("user32")]
+    public static extern bool PostMessage(IntPtr hwnd, int msg, IntPtr wparam, IntPtr lparam);
+    [DllImport("user32")]
+    public static extern int RegisterWindowMessage(string message);
+}
\ No newline at end of file
diff --git a/02_Windows_App/Perun_v1/01_Classes/Program.cs b/02_Windows_App/Perun_v1/01_Classes/Program.cs
index 0d3e1a5..2476321 100644
--- a/02_Windows_App/Perun_v1/01_Classes/Program.cs
+++ b/02_Windows_App/Perun_v1/01_Classes/Program.cs
@@ -1,4 +1,5 @@
 using System;
+using System.Threading;
 using System.Windows.Forms;
 
 namespace Perun_v1
@@ -9,24 +10,39 @@ namespace Perun_v1
         /// <summary>
         /// Główny punkt wejścia dla aplikacji.
         /// </summary>
+
+        // Mutex to block multiple instances
+        static Mutex mutex = new Mutex(true, "{5a710507-92e9-4664-9b91-918b8b82f107}");
         [STAThread]
 
-    
         static void Main()
         {
-            Application.EnableVisualStyles();
-            Application.SetCompatibleTextRenderingDefault(false);
-
-            Application.ApplicationExit += new EventHandler(Application_ApplicationExit);
-
-            void Application_ApplicationExit(object sender, EventArgs e)
+            if (mutex.WaitOne(TimeSpan.Zero, true))
             {
-                Properties.Settings.Default.Save();
-            }
+                Application.EnableVisualStyles();
+                Application.SetCompatibleTextRenderingDefault(false);
+                Application.ApplicationExit += new EventHandler(Application_ApplicationExit);
 
-            Application.Run(new form_Main());
+                void Application_ApplicationExit(object sender, EventArgs e)
+                {
+                    Properties.Settings.Default.Save();
+                }
+                Application.Run(new form_Main());
+                mutex.ReleaseMutex();
+            }
+            else
+            {
+                // send our Win32 message to make the currently running instance
+                // jump on top of all the other windows
+                NativeMethods.PostMessage(
+                    (IntPtr)NativeMethods.HWND_BROADCAST,
+                    NativeMethods.WM_SHOWME,
+                    IntPtr.Zero,
+                    IntPtr.Zero);
+                MessageBox.Show("Only one instance is allowed.");
+            }
         }
 
-       
+
     }
 }
diff --git a/02_Windows_App/Perun_v1/02_Forms/form_Main.cs b/02_Windows_App/Perun_v1/02_Forms/form_Main.cs
index 9ea419c..18de3ce 100644
--- a/02_Windows_App/Perun_v1/02_Forms/form_Main.cs
+++ b/02_Windows_App/Perun_v1/02_Forms/form_Main.cs
@@ -544,5 +544,27 @@ namespace Perun_v1
                 }
             }
         }
+
+        protected override void WndProc(ref Message m)
+        {
+            if (m.Msg == NativeMethods.WM_SHOWME)
+            {
+                ShowMe();
+            }
+            base.WndProc(ref m);
+        }
+        private void ShowMe()
+        {
+            if (WindowState == FormWindowState.Minimized)
+            {
+                WindowState = FormWindowState.Normal;
+            }
+            // get our current "TopMost" value (ours will always be false though)
+            bool top = TopMost;
+            // make our form jump to the top of everything
+            TopMost = true;
+            // set it back to whatever it was
+            TopMost = top;
+        }
     }
 }
diff --git a/02_Windows_App/Perun_v1/Perun_v1.csproj b/02_Windows_App/Perun_v1/Perun_v1.csproj
index f867364..bcda4e7 100644
--- a/02_Windows_App/Perun_v1/Perun_v1.csproj
+++ b/02_Windows_App/Perun_v1/Perun_v1.csproj
@@ -32,7 +32,7 @@
     <SuiteName>Perun</SuiteName>
     <CreateWebPageOnPublish>true</CreateWebPageOnPublish>
     <WebPage>Perun.htm</WebPage>
-    <ApplicationRevision>1</ApplicationRevision>
+    <ApplicationRevision>2</ApplicationRevision>
     <ApplicationVersion>0.4.0.%2a</ApplicationVersion>
     <UseApplicationTrust>false</UseApplicationTrust>
     <CreateDesktopShortcut>true</CreateDesktopShortcut>
@@ -116,6 +116,7 @@
     <Reference Include="System.Xml" />
   </ItemGroup>
   <ItemGroup>
+    <Compile Include="01_Classes\NativeMethods.cs" />
     <Compile Include="02_Forms\form_Main.cs">
       <SubType>Form</SubType>
     </Compile>