diff --git a/addons/check_id_in_db.php b/addons/check_id_in_db.php
new file mode 100644
index 0000000..24f0e56
--- /dev/null
+++ b/addons/check_id_in_db.php
@@ -0,0 +1,12 @@
+<?php
+
+$result = $pdo->prepare('SELECT id FROM categories');
+$result->execute();
+$checkId = $result->fetchAll();
+
+$id_array = array();
+
+foreach($checkId as $id_in_database)
+{
+    array_push($id_array, $id_in_database['id']);
+}
\ No newline at end of file
diff --git a/index.php b/index.php
index 67a3265..1b8b442 100644
--- a/index.php
+++ b/index.php
@@ -1,6 +1,7 @@
 <?php
-include('db/pdo.php');
-include('utils/utils.php');
+require('db/pdo.php');
+require('utils/utils.php');
+require('addons/check_id_in_db.php');
 
 if(array_key_exists('v', $_GET)) {
 	$module = $_GET['v'];
diff --git a/modules/categories.php b/modules/categories.php
index 6c35fed..ddb9abf 100644
--- a/modules/categories.php
+++ b/modules/categories.php
@@ -17,7 +17,6 @@
     <?php
     foreach($categories as $category) {
     ?>
-
         <tr>
             <td><?php echo $category['id'];?></td>
             <td><?php echo $category['name'];?></td>
@@ -25,9 +24,8 @@
                 <a href="index.php?v=edit_category&id=<?php echo $category['id'] ?>" class="btn btn-success">Edit</a>
             </td>
             <td>
-                <a href="index.php?v=delete_category&id=<?php echo $category['id'] ?>" class="btn btn-danger">Delete</a>
+                <a onclick="return confirm('Usunąć ten rekord?')" href="index.php?v=delete_category&id=<?php echo $category['id'] ?>" class="btn btn-danger">Delete</a>
             </td>
         </tr>
-
     <?php } ?>
-</table>
\ No newline at end of file
+</table>
diff --git a/modules/delete_category.php b/modules/delete_category.php
index a388f34..d48c576 100644
--- a/modules/delete_category.php
+++ b/modules/delete_category.php
@@ -1,9 +1,10 @@
 <?php
-if(!isset($_GET['id'])) {
-	header('location: index.php?v=categories');
-}
 
-$result = $pdo->prepare('DELETE FROM categories WHERE id = :id');
-$result->bindParam(':id', $_GET['id']);
-$result->execute();
-header('location: index.php?v=categories');
\ No newline at end of file
+if(!isset($_GET['id']) || !in_array($_GET['id'], $id_array)) {
+	header('location: index.php?v=categories');
+}else{
+    $result = $pdo->prepare('DELETE FROM categories WHERE id = :id');
+    $result->bindParam(':id', $_GET['id']);
+    $result->execute();
+    header('location: index.php?v=categories');
+}
\ No newline at end of file
diff --git a/modules/edit_category.php b/modules/edit_category.php
index c992f28..95a4fc0 100644
--- a/modules/edit_category.php
+++ b/modules/edit_category.php
@@ -9,14 +9,15 @@
 	header('location: index.php?v=categories');
 }
 
-if(!isset($_GET['id'])) {
-	header('location: index.php?v=categories');
+if(!isset($_GET['id']) || !in_array($_GET['id'], $id_array )) {
+    header('location: index.php?v=categories');
+}else{
+    $result = $pdo->prepare('SELECT * FROM categories WHERE id = :id');
+    $result->bindParam(':id', $_GET['id']);
+    $result->execute();
+    $category = $result->fetch();
 }
 
-$result = $pdo->prepare('SELECT * FROM categories WHERE id = :id');
-$result->bindParam(':id', $_GET['id']);
-$result->execute();
-$category = $result->fetch();
 
 ?>