diff --git a/_test/types/UserTest.php b/_test/types/UserTest.php
index fe072905..a5848541 100644
--- a/_test/types/UserTest.php
+++ b/_test/types/UserTest.php
@@ -35,7 +35,19 @@ public function test_validate_success()
 
     public function test_ajax()
     {
-        global $INPUT;
+        global $INFO, $INPUT, $USERINFO;
+        include(__DIR__ . '/../../conf/default.php');
+        $default_allow_autocomplete = $conf['allow_username_autocomplete'];
+        unset($conf);
+
+        global $conf;
+        $conf['plugin']['struct']['allow_username_autocomplete'] = $default_allow_autocomplete;
+        $_SERVER['REMOTE_USER'] = 'john';
+        $USERINFO['name'] = 'John Smith';
+        $USERINFO['mail'] = 'john.smith@example.com';
+        $USERINFO['grps'] = ['user', 'test'];
+        //update info array
+        $INFO['userinfo'] = $USERINFO;
 
         $user = new User(
             [
@@ -56,6 +68,21 @@ public function test_ajax()
         $INPUT->set('search', 'd'); // under mininput
         $this->assertEquals([], $user->handleAjax());
 
+        // Check restrictions on who can access username data are respected
+        $conf['plugin']['struct']['allow_username_autocomplete'] = 'john';
+        $INPUT->set('search', 'dent');
+        $this->assertEquals([['label' => 'Arthur Dent [testuser]', 'value' => 'testuser']], $user->handleAjax());
+
+        $conf['plugin']['struct']['allow_username_autocomplete'] = '@user';
+        $INPUT->set('search', 'dent');
+        $this->assertEquals([['label' => 'Arthur Dent [testuser]', 'value' => 'testuser']], $user->handleAjax());
+
+        $conf['plugin']['struct']['allow_username_autocomplete'] = '@not_in_group,not_this_user';
+        $INPUT->set('search', 'dent');
+        $this->assertEquals([], $user->handleAjax());
+
+        $conf['plugin']['struct']['allow_username_autocomplete'] = $default_allow_autocomplete;
+
         $user = new User(
             [
                 'autocomplete' => [
diff --git a/conf/default.php b/conf/default.php
index e41ca5ca..70b365b2 100644
--- a/conf/default.php
+++ b/conf/default.php
@@ -4,3 +4,4 @@
 $conf['topoutput'] = 0;
 $conf['disableDeleteSerial'] = 0;
 $conf['show_not_found'] = 1;
+$conf['allow_username_autocomplete'] = '@ALL';
diff --git a/conf/metadata.php b/conf/metadata.php
index 5a131dfa..cccebccf 100644
--- a/conf/metadata.php
+++ b/conf/metadata.php
@@ -4,3 +4,4 @@
 $meta['topoutput'] = ['onoff'];
 $meta['disableDeleteSerial'] = ['onoff'];
 $meta['show_not_found'] = ['onoff'];
+$meta['allow_username_autocomplete'] = ['string'];
diff --git a/lang/en/settings.php b/lang/en/settings.php
index eae3f50b..fe9bfff9 100644
--- a/lang/en/settings.php
+++ b/lang/en/settings.php
@@ -4,3 +4,4 @@
 $lang['topoutput'] = 'Display data at the top of the page';
 $lang['disableDeleteSerial'] = 'Disable delete button for serial data';
 $lang['show_not_found'] = 'Show the default text when no results are returned for struct value syntax';
+$lang['allow_username_autocomplete'] = 'Group, user or comma separated list user1,@group1,user2 to offer autocomplete suggestions for username data';
diff --git a/types/AbstractBaseType.php b/types/AbstractBaseType.php
index 973599da..fcd7c993 100644
--- a/types/AbstractBaseType.php
+++ b/types/AbstractBaseType.php
@@ -545,6 +545,18 @@ public function getLang($string)
         return $this->hlp->getLang($string);
     }
 
+    /**
+     * Convenience method to access plugin configurations
+     *
+     * @param string $string
+     * @return string
+     */
+    public function getConf($string)
+    {
+        if (is_null($this->hlp)) $this->hlp = plugin_load('helper', 'struct');
+        return $this->hlp->getConf($string);
+    }
+
     /**
      * With what comparator should dynamic filters filter this type?
      *
diff --git a/types/User.php b/types/User.php
index 93aa2c08..db929f0f 100644
--- a/types/User.php
+++ b/types/User.php
@@ -60,18 +60,29 @@ public function renderValue($value, \Doku_Renderer $R, $mode)
      * Autocompletion for user names
      *
      * @return array
-     * @todo should we have any security mechanism? Currently everybody can look up users
      */
     public function handleAjax()
     {
         /** @var AuthPlugin $auth */
         global $auth;
         global $INPUT;
+        global $_SERVER;
+        global $USERINFO;
 
         if (!$auth->canDo('getUsers')) {
             return [];
         }
 
+        if (
+            !auth_isMember(
+                $this->getConf('allow_username_autocomplete'),
+                $_SERVER['REMOTE_USER'],
+                (array) $USERINFO['grps']
+            )
+        ) {
+            return [];
+        }
+
         // check minimum length
         $lookup = trim($INPUT->str('search'));
         if (PhpString::strlen($lookup) < $this->config['autocomplete']['mininput']) return [];