diff --git a/README.md b/README.md
index a71d3f2..69c8632 100644
--- a/README.md
+++ b/README.md
@@ -3,7 +3,7 @@
 ## Introduction
 
 This plugin logs failed login attempts and requires users to go through
-a reCAPTCHA verification process when the number of failed attempts go
+a reCAPTCHA|hCaptcha verification process when the number of failed attempts go
 too high. It provides protection against automated attacks.
 
 Failed attempts are logged by IP and stored in a database table.
@@ -12,8 +12,8 @@ IPs are also released after a certain expire amount of time.
 
 ## Installation
 
-<big>**IMPORTANT: This plugin requires reCAPTCHA API keys to work properly.**</big>
-<br>These can be obtained from https://www.google.com/recaptcha.
+<big>**IMPORTANT: This plugin requires reCAPTCHA|hCaptcha API keys to work properly.**</big>
+<br>These can be obtained from https://www.google.com/recaptcha or https://dashboard.hcaptcha.com/.
 
 
 #### With Composer
@@ -44,15 +44,16 @@ the table `rcguard` accordingly.
 
 You may customize the following in the `config.inc.php` file:
 
-- the API version: `v3`, `v2invisible` or `v2`;
+- the API version: `v3`, `v2invisible`, `v2` or `v2hcaptcha`;
 - the v2 widget theme: `light` or `dark`;
 - the v2 widget size: `normal` or `compact`.
 
-For more information about the widget please check the [documentation about reCAPTCHA][recaptcha-doc].
+For more information about the widget please check the [documentation about reCAPTCHA][recaptcha-doc]
+or [documentation about hCaptcha][hcaptcha-doc].
 
 The plugin configuration file has several other options you may configure, please take at look.
 
-Since May 2018, you can define a proxy (anonymous or authenticated) to request the recaptcha widget.
+Since May 2018, you can define a proxy (anonymous or authenticated) to request the reCAPTCHA|hCaptcha widget.
 
 
 ## Supported databases
@@ -79,12 +80,13 @@ Email: [Diana Soares][email]
 [email]: mailto:diana.soares@gmail.com
 [dennylin]: https://github.com/dennylin93
 [recaptcha-doc]: https://developers.google.com/recaptcha/intro
+[hcaptcha-doc]: https://docs.hcaptcha.com/
 
 
 ## License
 
 This plugin is distributed under the GPL-3.0+ license.
 
-This plugin also contains a PHP library for reCAPTCHA that is
-distributed under its own license. See the library file for the exact details.
+This plugin also contains PHP libraries for reCAPTCHA and hCaptcha that is
+distributed under its own license. See the library files for the exact details.
 
diff --git a/config.inc.php.dist b/config.inc.php.dist
index 94616d4..d6843fb 100644
--- a/config.inc.php.dist
+++ b/config.inc.php.dist
@@ -12,21 +12,22 @@ $config['expire_time'] = 30;
 // Reset failure count after successfull login (see bratkartoffel/rcguard@670395e)
 $config['rcguard_reset_after_success'] = true;
 
-// reCAPTCHA API version and url
-$config['recaptcha_api_version'] = 'v2'; // v3 | v2 | v2invisible
-$config['recaptcha_api_url'] = 'https://www.google.com/recaptcha/api.js';
+// reCAPTCHA|hCaptcha API version and url
+$config['recaptcha_api_version'] = 'v2'; // v3 | v2 | v2invisible | v2hcaptcha
+$config['recaptcha_api_url'] = 'https://www.google.com/recaptcha/api.js'; // reCAPTCHA
+//$config['recaptcha_api_url'] = 'https://js.hcaptcha.com/1/api.js'; // hCaptcha
 
 // !!! DEPRECATED - not used anymore !!!
 //$config['recaptcha_api']        = 'http://www.google.com/recaptcha/api.js';
 //$config['recaptcha_api_secure'] = 'https://www.google.com/recaptcha/api.js';
 //$config['recaptcha_https']      = true;
 
-// Keys can be obtained from http://www.google.com/recaptcha/
+// Keys can be obtained from http://www.google.com/recaptcha/ or https://dashboard.hcaptcha.com/
 
-// reCAPTCHA site key
+// reCAPTCHA|hCaptcha site key
 $config['recaptcha_publickey'] = '';
 
-// reCAPTCHA secret key
+// reCAPTCHA|hCaptcha secret key
 $config['recaptcha_privatekey'] = '';
 
 // Send client IP to Google for reCAPTCHA verification
@@ -53,8 +54,9 @@ $config['recaptcha_size'] = 'normal';
 // Parameter expansion:
 // %r - Remote IP
 // %u - Username
-$config['recaptcha_log_success'] = 'Verification succeeded for %u. [%r]';
-$config['recaptcha_log_failure'] = 'Error: Verification failed for %u. [%r]';
+// %v - API version
+$config['recaptcha_log_success'] = 'Verification succeeded for %u. [%r] via %v';
+$config['recaptcha_log_failure'] = 'Error: Verification failed for %u. [%r] via %v';
 $config['recaptcha_log_unknown'] = 'Error: Unknown log type.';
 
 // Block IPv6 clients based on prefix length
diff --git a/lib/hcaptchalib.php b/lib/hcaptchalib.php
new file mode 100644
index 0000000..0e4f7cf
--- /dev/null
+++ b/lib/hcaptchalib.php
@@ -0,0 +1,196 @@
+<?php
+/**
+ * This is a PHP library that handles calling hCaptcha.
+ *    - See also
+ *          https://docs.hcaptcha.com/
+ *    - Get a hCaptcha Site/Secret Key
+ *          https://dashboard.hcaptcha.com/
+ *
+ * THIS IS AN ADJUSTED VERSION SUPPORTING hCaptcha
+ *
+ * based on recaptchalib.php (php_1.1.1)
+ *   from https://developers.google.com/recaptcha/docs/php
+ *
+ * @copyright Copyright (c) 2014, Google Inc.
+ * @link      http://www.google.com/recaptcha
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+/**
+ * hCaptcha client
+ */
+class ReCaptcha
+{
+    private static $version = "php_1.1.1";
+    private static $signupUrl = "https://dashboard.hcaptcha.com/";
+    private static $siteVerifyUrl = "https://hcaptcha.com/siteverify";
+    private $_secret;
+    private $_options;
+
+    /**
+     * Constructor.
+     *
+     * @param string $secret shared secret between site and ReCAPTCHA server.
+     * @param array  $extra_options Extra options to pass to the stream context.
+     */
+    function __construct($secret, $extra_options = null)
+    {
+        if (empty($secret)) {
+            die('To use hCaptcha you must get an API key from <a href="' .
+                self::$signupUrl . '">' . self::$signupUrl . '</a>');
+        }
+
+        $this->_secret = $secret;
+        $this->_options = $extra_options;
+    }
+
+
+    /**
+     * Submit the POST request with the specified parameters.
+     *
+     * @param array $params Request parameters
+     * @return string Body of the hCaptcha response
+     */
+    private function _submit($params)
+    {
+        // PHP 5.6.0 changed the way you specify the peer name for SSL context options.
+        // Using "CN_name" will still work, but it will raise deprecated errors.
+        $peer_key = version_compare(PHP_VERSION, '5.6.0', '<') ? 'CN_name' : 'peer_name';
+        $options  = array(
+            'http' => array(
+                'header' => "Content-type: application/x-www-form-urlencoded\r\n",
+                'method' => 'POST',
+                'content' => http_build_query($params, '', '&'),
+                // Force the peer to validate (not needed in 5.6.0+, but still works)
+                'verify_peer' => true,
+                $peer_key => 'hcaptcha.com',
+            )
+        );
+
+        if ($this->_options) {
+            $options = self::mergeOptions($options, $this->_options);
+        }
+
+        // REMEMBER: this is only for this kind of RequestMethod\Post
+        if (isset($options['http']['proxy'])
+            && strpos($options['http']['proxy'], 'tcp://') === false) {
+            $options['http']['proxy'] = 'tcp://' . $options['http']['proxy'];
+        }
+
+        $context = stream_context_create($options);
+        return file_get_contents(self::$siteVerifyUrl, false, $context);
+    }
+
+    /**
+     * Recursively merge options without appending values.
+     *
+     * @param  array  $opts1 Options array (the default options)
+     * @param  array  $opts2 Options array (the given options)
+     * @return array         The merged options
+     */
+    private static function mergeOptions($opts1, $opts2)
+    {
+        if (is_array($opts2)) {
+            foreach ($opts2 as $key => $val) {
+                $opts1[$key] = (
+                    is_array($val) && isset($opts1[$key]) && is_array($opts1[$key])
+                    ? self::mergeOptions($opts1[$key], $val) : $val
+                );
+            }
+        }
+        return $opts1;
+    }
+
+    /**
+     * Calls the hCaptcha siteverify API to verify whether the user passes
+     * CAPTCHA test. (hCaptcha version php_1.1.1)
+     *
+     * @param string $response The value of 'h-captcha-response' in the submitted form.
+     * @param string $remoteIp The end user's IP address.
+     * @param string $sitekey assigned site key
+     * @return ReCaptchaResponse Response from the service.
+     */
+    public function verify($response, $remoteIp = null, $sitekey = null)
+    {
+        if (empty($response)) { // Discard empty solution submissions
+            return new ReCaptchaResponse(false, array('missing-input'));
+        }
+
+        $params = array('secret'   => $this->_secret,
+                        'sitekey'  => $sitekey,
+                        'remoteip' => $remoteIp,
+                        'response' => $response
+                        );
+
+        $rawResponse = $this->_submit($params);
+
+        return ReCaptchaResponse::fromJson($rawResponse);
+    }
+}
+
+
+/**
+ * The response returned from the service.
+ */
+class ReCaptchaResponse
+{
+    public $success;
+    public $errorCodes;
+
+    /**
+     * Constructor.
+     *
+     * @param boolean $success
+     * @param array $errorCodes
+     */
+    function __construct($success, $errorCodes=array())
+    {
+        $this->success = $success;
+        $this->errorCodes = $errorCodes;
+    }
+
+    /**
+     * Build the response from the expected JSON returned by the service.
+     *
+     * @param string $json
+     * @return ReCaptchaResponse
+     */
+    public static function fromJson($json)
+    {
+        $responseData = json_decode($json, true);
+
+        if (!$responseData) {
+            $reCaptchaResponse = new ReCaptchaResponse(false, array('invalid-json'));
+        }
+        else if (isset($responseData['success']) && $responseData['success'] == true) {
+            $reCaptchaResponse = new ReCaptchaResponse(true);
+        }
+        else if (isset($responseData['error-codes']) && is_array($responseData['error-codes'])) {
+            $reCaptchaResponse = new ReCaptchaResponse(false, $responseData['error-codes']);
+        }
+        else {
+            $reCaptchaResponse = new ReCaptchaResponse(false);
+        }
+
+        return $reCaptchaResponse;
+    }
+}
+
+?>
diff --git a/rcguard.php b/rcguard.php
index f6aaf6a..d9507e0 100644
--- a/rcguard.php
+++ b/rcguard.php
@@ -123,7 +123,14 @@ public function authenticate($args)
         }
 
         $msg = 'rcguard.recaptchaempty';
-        $response = rcube_utils::get_input_value('g-recaptcha-response', rcube_utils::INPUT_POST);
+
+        $api_version = $this->rc->config->get('recaptcha_api_version', 'v2');
+        $input_value = 'g-recaptcha-response';
+        if ($api_version == 'v2hcaptcha') {
+            $input_value = 'h-captcha-response';
+        };
+
+        $response = rcube_utils::get_input_value($input_value, rcube_utils::INPUT_POST);
 
         if ($response) {
             if ($this->verify_recaptcha($response, $client_ip)) {
@@ -310,12 +317,20 @@ private function show_recaptcha_v2invisible()
     private function show_recaptcha_v2($size = null)
     {
         $api = $this->rc->config->get('recaptcha_api_url');
-        $src = sprintf('%s?hl=%s', $api, $this->rc->user->language);
+        $lang = $this->rc->user->language;
+        $lang_territory_separator_pos = strpos($lang, '_');
+        if ($lang_territory_separator_pos > 0) {
+            // hCaptcha is not supporting 'territory' appendix
+            $lang = substr($lang, 0, $lang_territory_separator_pos);
+        };
+        $src = sprintf('%s?hl=%s', $api, $lang);
         $this->include_script($src);
 
+        $api_version = $this->rc->config->get('recaptcha_api_version', 'v2');
         $html = sprintf(
-            '<div class="g-recaptcha" ' .
+            '<div class="%s" ' .
             'data-sitekey="%s" data-theme="%s" data-size="%s"></div>',
+            ($api_version == 'v2hcaptcha') ? 'h-captcha' : 'g-recaptcha',
             $this->rc->config->get('recaptcha_publickey'),
             $this->rc->config->get('recaptcha_theme'),
             $size ?: $this->rc->config->get('recaptcha_size')
@@ -348,10 +363,20 @@ private function verify_recaptcha($response, $client_ip = null)
             }
         }
 
-        require_once $this->home . '/lib/recaptchalib.php';
+        $api_version = $this->rc->config->get('recaptcha_api_version', 'v2');
+        if ($api_version == 'v2hcaptcha') {
+            require_once $this->home . '/lib/hcaptchalib.php';
+        } else {
+            require_once $this->home . '/lib/recaptchalib.php';
+        };
 
         $reCaptcha = new ReCaptcha($config->get('recaptcha_privatekey'), $options);
-        $resp = $reCaptcha->verify($response, $client_ip);
+
+        if ($api_version == 'v2hcaptcha') {
+            $resp = $reCaptcha->verify($response, $client_ip, $config->get('recaptcha_publickey'));
+        } else {
+            $resp = $reCaptcha->verify($response, $client_ip);
+        };
 
         return $resp != null && $resp->success;
     }
@@ -379,7 +404,8 @@ private function log_recaptcha($log_type, $username)
         }
 
         if (!empty($log_entry)) {
-            $log_entry = str_replace(['%r', '%u'], [$client_ip, $username], $log_entry);
+            $api_version = $this->rc->config->get('recaptcha_api_version', 'v2');
+            $log_entry = str_replace(['%r', '%u', '%v'], [$client_ip, $username, $api_version], $log_entry);
             rcube::write_log('rcguard', $log_entry);
         }
     }