diff --git a/Makefile b/Makefile
index bbc24932f02590bedb29363748c0a046037fbae2..c7c936d360dc727d504892f8030c801d7d468a19 100644
--- a/Makefile
+++ b/Makefile
@@ -1,7 +1,7 @@
 BASE=buyer_assign_group
 PLUGINTYPE=vmcustom
 ZIPBASE=opentools_vm2
-VERSION=1.6
+VERSION=1.6.1
 
 PLUGINFILES=$(BASE).php $(BASE).script.php $(BASE).xml index.html
 
diff --git a/buyer_assign_group.php b/buyer_assign_group.php
index 64c21bdeb43d42694469e714830cf60894c4bea9..b46a27f2a7d83f7ec8dca1e3628db94afa673b84 100644
--- a/buyer_assign_group.php
+++ b/buyer_assign_group.php
@@ -356,16 +356,202 @@ class plgVmCustomBuyer_Assign_Group extends vmCustomPlugin {
 		}
 	}
 
-// 	function plgVmOnSelfCallBE($type, $name, &$output) {
-// 		if ($name != $this->_name || $type != 'vmcustom') return false;
-// 		vmDebug('plgVmOnSelfCallBE');
-// 		
-// 		$db = JFactory::getDBO();
-// 		$db->setQuery("SELECT * FROM `".$this->_tablename.";");
-// 		$val = $db->loadAssocList();
-// 		
-// 		JFactory::getApplication()->enqueueMessage("<pre>plgVmOnSelfCallBE, type=$type, name=$name, full database contents:".print_r($val,1)."</pre>", 'error');		
-// 	}
+    /**
+     * plgVmOnSelfCallBE ... Called to execute some plugin action in the backend (e.g. set/reset dl counter, show statistics etc.)
+     */
+    function plgVmOnSelfCallBE($type, $name, &$output) {
+        if ($name != $this->_name || $type != $this->_type) return false;
+        vmDebug('plgVmOnSelfCallBE');
+        $user = JFactory::getUser();
+        $authorized = ($user->authorise('core.admin','com_virtuemart') or
+                       $user->authorise('core.manage','com_virtuemart'));
+        $json = array();
+        $json['authorized'] = $authorized;
+        if (!$authorized) return FALSE;
+
+        $action = vRequest::getCmd('action');
+        $json['action'] = $action;
+        $json['success'] = 0; // default: unsuccessfull
+        switch ($action) {
+			case "check_update_access":
+				$order_number = vRequest::getString('order_number');
+				$order_pass = vRequest::getString('order_pass');
+				$json = $this->checkUpdateAccess($order_number, $order_pass, $json);
+				break;
+        }
+        
+        // Also return all messages (in HTML format!):
+        // Since we are in a JSON document, we have to temporarily switch the type 
+        // to HTML to make sure the html renderer is actually used
+        $document = JFactory::getDocument ();
+        $previoustype = $document->getType();
+        $document->setType('html');
+        $msgrenderer = $document->loadRenderer('message');
+        $json['messages'] = $msgrenderer->render('Message');
+        $document->setType($previoustype);
+
+        // WORKAROUND for broken (i.e. duplicate) content-disposition headers in Joomla 2.x:
+        // We request everything in raw and here send the headers for JSON and return
+        // the raw output in json format
+        $document =JFactory::getDocument();
+        $document->setMimeEncoding('application/json');
+        JResponse::setHeader('Content-Disposition','attachment;filename="opentools_update_access.json"');
+        $output = json_encode($json);
+    }
+    
+    protected function checkUpdateAccess($order_number, $order_pass, $json = array()) {
+		// First, extract the update server URL from the manifest, then load 
+		// the update XML from the update server, extract the download URL, 
+		// append the order number and password and check whether access is 
+		// possible.
+		$json['success'] = FALSE;
+		$xml = simplexml_load_file($this->_xmlFile);
+		if (!$xml || !isset($xml->updateservers)) {
+			JFactory::getApplication()->enqueueMessage(JText::sprintf('OPENTOOLS_XMLMANIFEST_ERROR', $this->_xmlFile), 'error');
+			return $json;
+		}
+		$updateservers = $xml->updateservers;
+		foreach ($updateservers->children() as $server) {
+			if ($server->getName()!='server') {
+				JFactory::getApplication()->enqueueMessage(JText::sprintf('OPENTOOLS_XMLMANIFEST_ERROR', $this->_xmlFile), 'error');
+				continue;
+			}
+			$updateurl = html_entity_decode((string)$server);
+			$updatescript = simplexml_load_file($updateurl);
+			if (!$updatescript) {
+				JFactory::getApplication()->enqueueMessage(JText::sprintf('OPENTOOLS_UPDATESCRIPT_ERROR', $updateurl), 'error');
+				continue;
+			}
+			$urls = $updatescript->xpath('/updates/update/downloads/downloadurl');
+			while (list( , $node) = each($urls)) {
+				$downloadurl = (string)($node);
+				if ($order_number) {
+					$downloadurl .= (parse_url($downloadurl, PHP_URL_QUERY) ? '&' : '?') . 'order_number=' . urlencode($order_number);
+				}
+				if ($order_pass) {
+					$downloadurl .= (parse_url($downloadurl, PHP_URL_QUERY) ? '&' : '?') . 'order_pass=' . urlencode($order_pass);
+				}
+				$downloadurl .= (parse_url($downloadurl, PHP_URL_QUERY) ? '&' : '?') . 'check_access=1';
+
+				$headers = get_headers($downloadurl);
+				list($version, $status_code, $msg) = explode(' ',$headers[0], 3);
+				
+				// Check the HTTP Status code
+				switch($status_code) {
+					case 200:
+						$json['success'] = TRUE;
+						JFactory::getApplication()->enqueueMessage($msg, 'message');
+						$this->setupUpdateCredentials($order_number, $order_pass);
+						break;
+					default:
+						JFactory::getApplication()->enqueueMessage($msg, 'error');
+						// Clear the credentials...
+						$this->setupUpdateCredentials("", "");
+						break;
+				}
+				$this->setAndSaveParams(array(
+					'update_credentials_checked'=>$json['success'],
+					'order_number' => $order_number,
+					'order_pass' => $order_pass,
+				));
+			}
+		}
+		return $json;
+    }
+
+    protected function setAndSaveParams($params) {
+		$db = JFactory::getDbo();
+		$query = $db->getQuery(true)
+			->select('extension_id')
+			->from('#__extensions')
+			->where('folder = '.$db->quote($this->_type))
+			->where('element = '.$db->quote($this->_name))
+			->where('type =' . $db->quote('plugin'))
+			->order('ordering');
+
+		$plugin = $db->setQuery($query)->loadObject();
+		if (!$plugin)
+			return;
+		$pluginId=$plugin->extension_id;
+		
+		foreach ($params as $param=>$parvalue) {
+			$this->params->set($param, $parvalue);
+		}
+		
+		$extensions = JTable::getInstance('extension');
+		$extensions->load($pluginId);
+		$extensions->bind(array('params' => $this->params->toString()));
+		
+		// check and store 
+		if (!$extensions->check()) {
+			$this->setError($extensions->getError());
+			return false;
+		}
+		if (!$extensions->store()) {
+			$this->setError($extensions->getError());
+			return false;
+		}
+    }
+
+
+	protected function setupUpdateCredentials($ordernumber, $orderpass) {
+		$db = JFactory::getDbo();
+		$query = $db->getQuery(true)
+			->select('extension_id AS id')
+			->from('#__extensions')
+			->where('folder = '.$db->quote($this->_type))
+			->where('element = '.$db->quote($this->_name))
+			->where('type =' . $db->quote('plugin'))
+			->order('ordering');
+
+		$plugin = $db->setQuery($query)->loadObject();
+		if (empty($plugin))
+			return;
+
+		$ordernumber = preg_replace("/[^-A-Za-z0-9_]/", '', $ordernumber);
+		$orderpass = preg_replace("/[^-A-Za-z0-9_]/", '', $orderpass);
+		
+		$extra_query = array();
+		if ($ordernumber!='') {
+			$extra_query[] = 'order_number='.preg_replace("/[^-A-Za-z0-9_]/", '', $ordernumber);
+		}
+		if ($orderpass!='') {
+			$extra_query[] = 'order_pass='.preg_replace("/[^-A-Za-z0-9_]/", '', $orderpass);
+		}
+		$extra_query = implode('&amp;', $extra_query);
+		
+		// The following code is based on Nicholas K. Dionysopoulos' Joomla Pull request:
+		//     https://github.com/joomla/joomla-cms/pull/2508
+		
+		// Load the update site record, if it exists
+		$db = JFactory::getDbo();
+		$query = $db->getQuery(true)
+			->select('update_site_id AS id')
+			->from($db->qn('#__update_sites_extensions'))
+			->where($db->qn('extension_id').' = '.$db->q($plugin->id));
+		$db->setQuery($query);
+		$updateSites = $db->loadObjectList();
+
+		foreach ($updateSites as $updateSite) {
+			// Update the update site record
+			$query = $db->getQuery(true)
+				->update($db->qn('#__update_sites'))
+				->set('extra_query = '.$db->q($extra_query))
+				->set('last_check_timestamp = 0')
+				->where($db->qn('update_site_id').' = '.$db->q($updateSite->id));
+			$db->setQuery($query);
+			$db->execute();
+
+			// Delete any existing updates (essentially flushes the updates cache for this update site)
+			$query = $db->getQuery(true)
+				->delete($db->qn('#__updates'))
+				->where($db->qn('update_site_id').' = '.$db->q($updateSite->id));
+			$db->setQuery($query);
+			$db->execute();
+		}
+		
+	}
+
 }
 
 // No closing tag
\ No newline at end of file
diff --git a/buyer_assign_group.xml b/buyer_assign_group.xml
index 56acbe69206c23113ef21541894eb8bad4051c57..59231b731d5bb0f39e1c95d6170045288154bc17 100644
--- a/buyer_assign_group.xml
+++ b/buyer_assign_group.xml
@@ -6,7 +6,7 @@
     <authorUrl>http://www.open-tools.net/</authorUrl>
     <copyright>Copyright (C) 2013-2014 Reinhold Kainhofer. All rights reserved.</copyright>
     <license>http://www.gnu.org/licenses/gpl.html GNU/GPL v3+</license>
-    <version>1.6</version>
+    <version>1.6.1</version>
     <description>VMCUSTOM_BUYER_GROUP_DESC</description>
     <files>
         <filename plugin="buyer_assign_group">buyer_assign_group.php</filename>
@@ -14,6 +14,7 @@
         <filename>index.html</filename>
         <folder>language</folder>
         <folder>elements</folder>
+        <folder>fields</folder>
     </files>
     <languages folder="language">
         <language tag="en-GB">en-GB/en-GB.plg_vmcustom_buyer_assign_group.ini</language>
@@ -34,4 +35,19 @@
         <param type="vmjpluginwarning" />
         <param name="purchased_status" type="vmorderstates" default="C,S" multiple="multiple" label="VMCUSTOM_BUYER_GROUP_STATUS" description="VMCUSTOM_BUYER_GROUP_STATUS_DESC"/>
     </params>
+	
+    <config>
+        <fields name="params">
+            <fieldset name="update_credentials" label="OPENTOOLS_FIELDSET_CREDENTIALS" addfieldpath="/plugins/vmcustom/downloads_for_sale/fields">
+                <field name="credentials_desc" type="spacer" label="OPENTOOLS_CREDENTIALS_DESC" />
+                <field name="order_number" type="text" default="" label="OPENTOOLS_ORDERNUMBER" description="OPENTOOLS_ORDERNUMBER_DESC"/>
+                <field name="order_pass" type="text" default="" label="OPENTOOLS_ORDERPASS" description="OPENTOOLS_ORDERPASS_DESC"/>
+				<field name="update_credentials_checked" type="vmUpdateCredentialsCheck" label="" ajaxurl="index.php?option=com_virtuemart&amp;view=plugin&amp;type=vmcustom&amp;name=buyer_assign_group&amp;format=raw" />
+            </fieldset>
+		</fields>
+    </config>
+	<updateservers>
+		<server type="extension" name="VM Customers to Joomla Groups Plugin Updates"><![CDATA[http://open-tools.net/UpdateServer/index.php?package=Joomla&amp;extension=BuyerAssignGroups&amp;file=extension.xml]]></server>
+	</updateservers>
+
 </extension>
diff --git a/fields/index.html b/fields/index.html
new file mode 100644
index 0000000000000000000000000000000000000000..e69de29bb2d1d6434b8b29ae775ad8c2e48c5391
diff --git a/fields/vmupdatecredentialscheck.php b/fields/vmupdatecredentialscheck.php
new file mode 100644
index 0000000000000000000000000000000000000000..d08397b1a162d02b78ba2551a79aa2e43957a3e4
--- /dev/null
+++ b/fields/vmupdatecredentialscheck.php
@@ -0,0 +1,161 @@
+<?php
+defined('_JEXEC') or die();
+/**
+ *
+ * @package    VirtueMart
+ * @subpackage Plugins  - Fields
+ * @author Reinhold Kainhofer, Open Tools
+ * @link http://www.open-tools.net
+ * @copyright Copyright (c) 2016 Reinhold Kainhofer. All rights reserved.
+ * @license http://www.gnu.org/copyleft/gpl.html GNU/GPL, see LICENSE.txt
+ * VirtueMart is free software. This version may have been modified pursuant
+ * to the GNU General Public License, and as distributed it includes or
+ * is derivative of works licensed under the GNU General Public License or
+ * other free or open source software licenses.
+ */
+ 
+defined('DS') or define('DS', DIRECTORY_SEPARATOR);
+if (!class_exists( 'VmConfig' )) 
+    require(JPATH_ROOT.DS.'administrator'.DS.'components'.DS.'com_virtuemart'.DS.'helpers'.DS.'config.php');
+VmConfig::loadConfig();
+
+class JFormFieldVmUpdateCredentialsCheck extends JFormField {
+    var $_name = 'vmUpdateCredentialsCheck';
+    
+	// VM2 on J2 works, VM3 on J3 works out of the box, but
+	// VM3 on J2 does NOT work by simply calling vmJsApi::jQuery, because
+	// the JS is never added to the page header, so we have to add this manually
+	public function loadjQuery() {
+		vmJsApi::jQuery();
+		// TODO: jquery::ui available only in J3:
+		if (version_compare(JVERSION, '3.0', 'lt')) {
+		} else {
+			JHtml::_('jquery.ui', array('core', 'sortable'));
+		}
+		// If we are on Joomla 2.5 and VM 3, manually add the script declarations 
+		// cached in vmJsApi to the document header:
+		if (version_compare(JVERSION, '3.0', 'lt') && defined('VM_VERSION') && VM_VERSION>=3) {
+			$document = JFactory::getDocument();
+			$scripts = vmJsApi::getJScripts();
+			foreach ($scripts as $name => $jsToAdd) {
+				if($jsToAdd['written']) continue;
+				$file = $jsToAdd['script'] ? $jsToAdd['script'] : $name;
+				
+				if(strpos($file,'/')!==0){
+					$file = vmJsApi::setPath($file,false,'');
+				} else if(strpos($file,'//')!==0){
+					$file = JURI::root(true).$file;
+				}
+
+				$ver = '';
+				if(!empty($jsToAdd['ver'])) $ver = '?vmver='.$jsToAdd['ver'];
+				$document->addScript( $file .$ver,"text/javascript",$jsToAdd['defer'],$jsToAdd['async'] );
+				vmJsApi::removeJScript($name);
+			}
+		}
+	}
+    
+    protected function getJavaScript() {
+		return "
+var credentials_ajaxurl = \"".$this->element["ajaxurl"]."\";
+var credentials_updateMessages = function(messages, area) {
+    jQuery( \"#system-message-container #system-message .\"+area+\"-message\").remove();
+    var newmessages = jQuery( messages ).find(\"div.alert, .message\").addClass(area+\"-message\");
+    if (!jQuery( \"#system-message-container #system-message\").length && newmessages.length) {
+        if (jQuery(newmessages).first().prop(\"tagName\")==\"dt\") { // Joomla 2.x:
+            jQuery( \"#system-message-container\" ).append( \"<dl id=\'system-message\'></div>\" );
+        } else {
+            jQuery( \"#system-message-container\" ).append( \"<div id=\'system-message\'></div>\" );
+        }
+    }
+    newmessages.appendTo( \"#system-message-container #system-message\");
+};
+
+var checkUpdateCredentialsError = function() {
+	alert (\"".JText::_('OPENTOOLS_CHECK_CREDENTIALS_ERROR')."\"); 
+}
+
+var checkUpdateCredentials = function () {
+	var ordernumber = jQuery('#jform_params_order_number').val();
+	var orderpass = jQuery('#jform_params_order_pass').val();
+	
+    var ajaxargs = {
+        type: \"POST\",
+		dataType: \"text\",
+        url: credentials_ajaxurl,
+        data: { 
+			action: \"check_update_access\",
+			order_number: ordernumber, 
+			order_pass: orderpass
+		},
+		
+		success: function ( json ) {
+			try {
+				json = jQuery.parseJSON(json);
+				credentials_updateMessages(json['messages'], 'ordernumber');
+			} catch (e) {
+				checkUpdateCredentialsError();
+				return;
+			}
+			var success=0;
+			if (json.success>0) {
+				success=1;
+			}
+			jQuery('#update_credentials_hidden_checked').val(success);
+			jQuery('.credentials_checked')
+				.removeClass('credentials_checked_0')
+				.removeClass('credentials_checked_1')
+				.addClass('credentials_checked_'+success);
+		},
+		error: function() { checkUpdateCredentialsError(); },
+		complete: function() {  },
+	};
+	jQuery.ajax(ajaxargs);
+};
+jQuery(document).ready (function () {
+	jQuery('#jform_params_order_number').focusout(checkUpdateCredentials);
+	jQuery('#jform_params_order_pass').focusout(checkUpdateCredentials);
+});
+
+";
+    }
+    
+    protected function getCSS() {
+		return "
+div.credentials_checked {
+	padding: 10px 5px;
+    float: left;
+    clear: left;
+    display: block;
+    width: 100%;
+}
+div.credentials_checked_0 {
+	background-color: #FFD0D0;
+}
+div.credentials_checked_1 {
+	background-color: #D0FFD0;
+}
+a#credentials_check {
+}
+
+";
+    }
+	protected function getInput() {
+		// Tell the user that automatic updates are not available in Joomla 2.5:
+		if (version_compare(JVERSION, '3.0', 'lt')) {
+			JFactory::getApplication()->enqueueMessage(JText::_('OPENTOOLS_COMMERCIAL_UPDATES_J25'), 'warning');
+		}
+
+		$this->loadjQuery();
+		
+		$doc = JFactory::getDocument();
+		$doc->addScriptDeclaration($this->getJavaScript());
+		$doc->addStyleDeclaration($this->getCSS());
+		
+		if ($this->value!=1) {
+			$this->value=0;
+		}
+// 		if ($this->value==1) {
+		return "<input type='hidden' id=\"update_credentials_hidden_checked\" name='".$this->name."' value='".$this->value."' /><div class='credentials_checked credentials_checked_".$this->value."'><a href=\"#\" class=\"btn btn-info credentials_check\" id=\"credentials_check\" onclick=\"checkUpdateCredentials()\" >".JText::_('OPENTOOLS_CHECK_CREDENTIALS')."</a></div>";
+	}
+}
diff --git a/language/en-GB/en-GB.plg_vmcustom_buyer_assign_group.ini b/language/en-GB/en-GB.plg_vmcustom_buyer_assign_group.ini
index 63249c19ff57600e99a2e8e968b9c5d4d70c5567..a929f75f1bcc1cc0e7993ed75cc326318b1727a5 100644
--- a/language/en-GB/en-GB.plg_vmcustom_buyer_assign_group.ini
+++ b/language/en-GB/en-GB.plg_vmcustom_buyer_assign_group.ini
@@ -13,4 +13,17 @@ VMCUSTOM_BUYER_GROUP_JOOMLA_REMOVE="Remove from Joomla Usergroups:"
 VMCUSTOM_BUYER_GROUP_SHOPPER="Add to VM Shoppergroups:"
 VMCUSTOM_BUYER_GROUP_SHOPPER_REMOVE="Remove from VM Shoppergroups:"
 
-VMCUSTOM_BUYER_GROUP_NO_UID="Not logged in as Joomla and VirtueMart user, unable to add to user groups. Please contact the vendor."
\ No newline at end of file
+VMCUSTOM_BUYER_GROUP_NO_UID="Not logged in as Joomla and VirtueMart user, unable to add to user groups. Please contact the vendor."
+
+
+OPENTOOLS_FIELDSET_CREDENTIALS="Update credentials"
+OPENTOOLS_CREDENTIALS_DESC="Please enter your order number and the order password, which can be found in the order confirmation mail you received after your purchase at <a href="https://www.open-tools.net/">open-tools.net</a>. If you do not enter a valid combination, the plugin will continue to work, but automatic updates will only be provided with a valid order number and password."
+OPENTOOLS_ORDERNUMBER="Order number:"
+OPENTOOLS_ORDERNUMBER_DESC="Please enter the order number of your purchase at open-tools.net to get access to automatic updates. If no valid order number and password is entered, the plugin will still work, but automatic updates will not be available."
+OPENTOOLS_ORDERPASS="Order password:"
+OPENTOOLS_ORDERPASS_DESC="Please enter the order password of your purchase at open-tools.net to get access to automatic updates. If no valid order number and password is entered, the plugin will still work, but automatic updates will not be available."
+OPENTOOLS_CHECK_CREDENTIALS="Check and save update credentials"
+OPENTOOLS_CHECK_CREDENTIALS_ERROR="Unable to check the download credentials. Please make sure that the plugin is enabled in your Joomla installation!"
+OPENTOOLS_XMLMANIFEST_ERROR="Unable to load the plugin manifest file (%s)"
+OPENTOOLS_UPDATESCRIPT_ERROR="Unable to load the update information from the update server (%s)"
+OPENTOOLS_COMMERCIAL_UPDATES_J25="Automatic updates of commercial Joomla extensions are not available in Joomla 2.5 (only in Joomla 3.x). Please check the software developer's homepage and manually install updates."
diff --git a/releases/plg_opentools_vm2_buyer_assign_group_v1.6.1.zip b/releases/plg_opentools_vm2_buyer_assign_group_v1.6.1.zip
new file mode 100644
index 0000000000000000000000000000000000000000..28af23e36df27a1fa350c002b2ebac9300158353
Binary files /dev/null and b/releases/plg_opentools_vm2_buyer_assign_group_v1.6.1.zip differ