diff --git a/_test/helper.test.php b/_test/helper.test.php
index 18e8f5e..3e79923 100644
--- a/_test/helper.test.php
+++ b/_test/helper.test.php
@@ -5,12 +5,15 @@ class helper_plugin_captcha_public extends helper_plugin_captcha {
     public function get_field_in() {
         return $this->field_in;
     }
+
     public function get_field_sec() {
         return $this->field_sec;
     }
+
     public function get_field_hp() {
         return $this->field_hp;
     }
+
     public function storeCaptchaCookie($fixed, $rand) {
         parent::storeCaptchaCookie($fixed, $rand);
     }
@@ -90,10 +93,57 @@ public function testGenerate() {
 
         $rand = 0;
         $code = $helper->_generateCAPTCHA($helper->_fixedIdent(), $rand);
-        $newcode = $helper->_generateCAPTCHA($helper->_fixedIdent().'X', $rand);
+        $newcode = $helper->_generateCAPTCHA($helper->_fixedIdent() . 'X', $rand);
         $this->assertNotEquals($newcode, $code);
-        $newcode = $helper->_generateCAPTCHA($helper->_fixedIdent(), $rand+0.1);
+        $newcode = $helper->_generateCAPTCHA($helper->_fixedIdent(), $rand + 0.1);
         $this->assertNotEquals($newcode, $code);
     }
 
+    public function testCleanup() {
+        // we need a complete fresh environment:
+        $this->setUpBeforeClass();
+
+        global $conf;
+        $path = $conf['tmpdir'] . '/captcha/';
+        $today = "$path/" . date('Y-m-d');
+
+        $helper = new helper_plugin_captcha_public();
+
+        // nothing at all
+        $dirs = glob("$path/*");
+        $this->assertEquals(array(), $dirs);
+
+        // store a cookie
+        $helper->storeCaptchaCookie('test', 0);
+
+        // nothing but today's data
+        $dirs = glob("$path/*");
+        $this->assertEquals(array($today), $dirs);
+
+        // add some fake cookies
+        io_saveFile("$path/2017-01-01/foo.cookie", '');
+        io_saveFile("$path/2017-01-02/foo.cookie", '');
+        io_saveFile("$path/2017-01-03/foo.cookie", '');
+        io_saveFile("$path/2017-01-04/foo.cookie", '');
+
+        // all directories there
+        $dirs = glob("$path/*");
+        $this->assertEquals(
+            array(
+                "$path/2017-01-01",
+                "$path/2017-01-02",
+                "$path/2017-01-03",
+                "$path/2017-01-04",
+                $today
+            ),
+            $dirs
+        );
+
+        // clean up
+        $helper->_cleanCaptchaCookies();
+
+        // nothing but today's data
+        $dirs = glob("$path/*");
+        $this->assertEquals(array($today), $dirs);
+    }
 }
diff --git a/action.php b/action.php
index 6fdf2f2..b775015 100644
--- a/action.php
+++ b/action.php
@@ -70,6 +70,15 @@ public function register(Doku_Event_Handler $controller) {
                 array()
             );
         }
+
+        // clean up captcha cookies
+        $controller->register_hook(
+            'INDEXER_TASKS_RUN',
+            'AFTER',
+            $this,
+            'handle_indexer',
+            array()
+        );
     }
 
     /**
@@ -195,5 +204,20 @@ public function handle_form_output(Doku_Event $event, $param) {
         $event->data->insertElement($pos + 1, $out);
     }
 
+    /**
+     * Clean cookies once per day
+     */
+    public function handle_indexer(Doku_Event $event, $param) {
+        $lastrun = getCacheName('captcha', '.captcha');
+        $last = @filemtime($lastrun);
+        if(time() - $last < 24 * 60 * 60) return;
+
+        /** @var helper_plugin_captcha $helper */
+        $helper = plugin_load('helper', 'captcha');
+        $helper->_cleanCaptchaCookies();
+
+        $event->preventDefault();
+        $event->stopPropagation();
+    }
 }
 
diff --git a/helper.php b/helper.php
index b745b54..5a7e999 100644
--- a/helper.php
+++ b/helper.php
@@ -6,7 +6,7 @@
 
 // must be run within Dokuwiki
 if(!defined('DOKU_INC')) die();
-if(!defined('DOKU_PLUGIN')) define('DOKU_PLUGIN', DOKU_INC.'lib/plugins/');
+if(!defined('DOKU_PLUGIN')) define('DOKU_PLUGIN', DOKU_INC . 'lib/plugins/');
 
 /**
  * Class helper_plugin_captcha
@@ -145,7 +145,7 @@ public function check($msg = true) {
     }
 
     /**
-     * Get the path where a capture cookie would be stored
+     * Get the path where a captcha cookie would be stored
      *
      * We use a daily temp directory which is easy to clean up
      *
@@ -160,6 +160,21 @@ protected function getCaptchaCookiePath($fixed, $rand) {
         return $path;
     }
 
+    /**
+     * remove all outdated captcha cookies
+     */
+    public function _cleanCaptchaCookies() {
+        global $conf;
+        $path = $conf['tmpdir'] . '/captcha/';
+        $dirs = glob("$path/*", GLOB_ONLYDIR);
+        $today = date('Y-m-d');
+        foreach($dirs as $dir) {
+            if(basename($dir) === $today) continue;
+            if(!preg_match('/\/captcha\//', $dir)) continue; // safety net
+            io_rmdir($dir, true);
+        }
+    }
+
     /**
      * Creates a one time captcha cookie
      *
@@ -210,9 +225,9 @@ public function _fixedIdent() {
         global $ID;
         $lm = @filemtime(wikiFN($ID));
         $td = date('Y-m-d');
-        return auth_browseruid().
-        auth_cookiesalt().
-        $ID.$lm.$td;
+        return auth_browseruid() .
+            auth_cookiesalt() .
+            $ID . $lm . $td;
     }
 
     /**