diff --git a/apps/pc_backend/lib/myUser.class.php b/apps/pc_backend/lib/myUser.class.php
index 5f528fe..528de7b 100644
--- a/apps/pc_backend/lib/myUser.class.php
+++ b/apps/pc_backend/lib/myUser.class.php
@@ -8,7 +8,7 @@
  * file and the NOTICE file that were distributed with this source code.
  */
 
-class myUser extends sfBasicSecurityUser
+class myUser extends opBaseSecurityUser
 {
   public function initialize(sfEventDispatcher $dispatcher, sfStorage $storage, $options = array())
   {
diff --git a/config/ProjectConfiguration.class.php.sample b/config/ProjectConfiguration.class.php.sample
index 78e7b83..1064ca3 100644
--- a/config/ProjectConfiguration.class.php.sample
+++ b/config/ProjectConfiguration.class.php.sample
@@ -15,8 +15,16 @@ class ProjectConfiguration extends sfProjectConfiguration
     $this->enableAllPluginsExcept(array('sfCompat10Plugin'));
     $this->setIncludePath();
 
-    //HTTP proxy to use when downloading plugin packages
+    // HTTP proxy to use when downloading plugin packages
     sfConfig::set('op_http_proxy', null);
+
+    // セッションデータにサイト特有の識別子を含めるかどうか
+    // Configuration of using site_identifier in session data
+    sfConfig::set('op_check_session_site_identifier', true);
+
+    // In default, OpenPNE saves session data file to default session.save_path.
+    // But in some cases, you may need to change the session save path:
+    // session_save_path('/tmp');
   }
 
   public function setIncludePath()
diff --git a/data/version.php b/data/version.php
index 30b5ff5..1d992a5 100644
--- a/data/version.php
+++ b/data/version.php
@@ -10,5 +10,5 @@
 
 if (!defined('OPENPNE_VERSION'))
 {
-  define('OPENPNE_VERSION', '3.0.8.1');
+  define('OPENPNE_VERSION', '3.0.8.2');
 }
diff --git a/lib/user/opBaseSecurityUser.class.php b/lib/user/opBaseSecurityUser.class.php
new file mode 100644
index 0000000..0eee520
--- /dev/null
+++ b/lib/user/opBaseSecurityUser.class.php
@@ -0,0 +1,88 @@
+<?php
+
+/**
+ * This file is part of the OpenPNE package.
+ * (c) OpenPNE Project (http://www.openpne.jp/)
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file and the NOTICE file that were distributed with this source code.
+ */
+
+/**
+ * The base class of the all security user classes for OpenPNE.
+ *
+ * @package    OpenPNE
+ * @subpackage user
+ * @author     Kousuke Ebihara <ebihara@php.net>
+ */
+abstract class opBaseSecurityUser extends sfBasicSecurityUser
+{
+  const SITE_IDENTIFIER_NAMESPACE = 'OpenPNE/user/opSecurityUser/site_identifier';
+
+  public function initialize(sfEventDispatcher $dispatcher, sfStorage $storage, $options = array())
+  {
+    if (!isset($options['session_namespaces']))
+    {
+      $options['session_namespaces'] = array(
+        self::SITE_IDENTIFIER_NAMESPACE,
+        self::LAST_REQUEST_NAMESPACE,
+        self::AUTH_NAMESPACE,
+        self::CREDENTIAL_NAMESPACE,
+        self::ATTRIBUTE_NAMESPACE,
+      );
+    }
+
+    parent::initialize($dispatcher, $storage, $options);
+
+    if (!$this->isValidSiteIdentifier())
+    {
+      // This session is not for this site.
+      $this->logout();
+
+      // So we need to clear all data of the current session because they might be tainted by attacker.
+      // If OpenPNE uses that tainted data, it may cause limited session fixation attack.
+      $this->clearSessionData();
+
+      return null;
+    }
+  }
+
+  abstract public function logout();
+
+  public function clearSessionData()
+  {
+    // remove data in storage
+    foreach ($this->options['session_namespaces'] as $v)
+    {
+      $this->storage->remove($v);
+    }
+
+    // remove attribtues
+    $this->attributeHolder->clear();
+  }
+
+  public function isValidSiteIdentifier()
+  {
+    if (!sfConfig::get('op_check_session_site_identifier', true))
+    {
+      return true;
+    }
+
+    return ($this->generateSiteIdentifier() === $this->storage->read(self::SITE_IDENTIFIER_NAMESPACE));
+  }
+
+  public function generateSiteIdentifier()
+  {
+    $request = sfContext::getInstance()->getRequest();
+    $identifier = $request->getUriPrefix().$request->getRelativeUrlRoot();
+
+    return $identifier;
+  }
+
+  public function shutdown()
+  {
+    $this->storage->write(self::SITE_IDENTIFIER_NAMESPACE, $this->generateSiteIdentifier());
+
+    parent::shutdown();
+  }
+}
diff --git a/lib/user/sfOpenPNESecurityUser.class.php b/lib/user/sfOpenPNESecurityUser.class.php
index 02d884f..961eee4 100644
--- a/lib/user/sfOpenPNESecurityUser.class.php
+++ b/lib/user/sfOpenPNESecurityUser.class.php
@@ -15,7 +15,7 @@
  * @subpackage user
  * @author     Kousuke Ebihara <ebihara@tejimaya.com>
  */
-class sfOpenPNESecurityUser extends sfBasicSecurityUser
+class sfOpenPNESecurityUser extends opBaseSecurityUser
 {
   protected $authAdapter = null;