diff --git a/lib/private/Setup.php b/lib/private/Setup.php
index 196ae8a8bc..23c66f98b7 100644
--- a/lib/private/Setup.php
+++ b/lib/private/Setup.php
@@ -367,7 +367,7 @@ class Setup {
 			\OC_User::login($username, $password);
 
 			//guess what this does
-			\OC_Installer::installShippedApps();
+			Installer::installShippedApps();
 
 			// create empty file in data dir, so we can later find
 			// out that this is indeed an ownCloud data directory
diff --git a/lib/private/Updater.php b/lib/private/Updater.php
index 093ebebbbe..7ca3cd0936 100644
--- a/lib/private/Updater.php
+++ b/lib/private/Updater.php
@@ -36,7 +36,6 @@ namespace OC;
 use OC\Hooks\BasicEmitter;
 use OC\IntegrityCheck\Checker;
 use OC_App;
-use OC_Installer;
 use OCP\IConfig;
 use OC\Setup;
 use OCP\ILogger;
@@ -251,7 +250,7 @@ class Updater extends BasicEmitter {
 
 			// install new shipped apps on upgrade
 			OC_App::loadApps('authentication');
-			$errors = OC_Installer::installShippedApps(true);
+			$errors = Installer::installShippedApps(true);
 			foreach ($errors as $appId => $exception) {
 				/** @var \Exception $exception */
 				$this->log->logException($exception, ['app' => $appId]);
@@ -443,11 +442,11 @@ class Updater extends BasicEmitter {
 	private function upgradeAppStoreApps(array $disabledApps) {
 		foreach($disabledApps as $app) {
 			try {
-				if (OC_Installer::isUpdateAvailable($app)) {
+				if (Installer::isUpdateAvailable($app)) {
 					$ocsId = \OC::$server->getConfig()->getAppValue($app, 'ocsid', '');
 
 					$this->emit('\OC\Updater', 'upgradeAppStoreApp', array($app));
-					OC_Installer::updateAppByOCSId($ocsId);
+					Installer::updateAppByOCSId($ocsId);
 				}
 			} catch (\Exception $ex) {
 				$this->log->logException($ex, ['app' => 'core']);
diff --git a/lib/private/legacy/app.php b/lib/private/legacy/app.php
index a1d4b7ce26..42bb441228 100644
--- a/lib/private/legacy/app.php
+++ b/lib/private/legacy/app.php
@@ -46,6 +46,7 @@
  */
 use OC\App\DependencyAnalyzer;
 use OC\App\Platform;
+use OC\Installer;
 use OC\OCSClient;
 use OC\Repair;
 
@@ -304,7 +305,7 @@ class OC_App {
 	 */
 	public static function enable($app, $groups = null) {
 		self::$enabledAppsCache = array(); // flush
-		if (!OC_Installer::isInstalled($app)) {
+		if (!Installer::isInstalled($app)) {
 			$app = self::installApp($app);
 		}
 
@@ -340,7 +341,7 @@ class OC_App {
 			// Replace spaces in download link without encoding entire URL
 			$download['downloadlink'] = str_replace(' ', '%20', $download['downloadlink']);
 			$info = array('source' => 'http', 'href' => $download['downloadlink'], 'appdata' => $appData);
-			$app = OC_Installer::installApp($info);
+			$app = Installer::installApp($info);
 		}
 		return $app;
 	}
@@ -354,7 +355,7 @@ class OC_App {
 			return false;
 		}
 
-		return OC_Installer::removeApp($app);
+		return Installer::removeApp($app);
 	}
 
 	/**
@@ -827,7 +828,7 @@ class OC_App {
 					$info['removable'] = true;
 				}
 
-				$info['update'] = ($includeUpdateInfo) ? OC_Installer::isUpdateAvailable($app) : null;
+				$info['update'] = ($includeUpdateInfo) ? Installer::isUpdateAvailable($app) : null;
 
 				$appPath = self::getAppPath($app);
 				if($appPath !== false) {
@@ -1073,7 +1074,7 @@ class OC_App {
 			if ($appData && version_compare($shippedVersion, $appData['version'], '<')) {
 				$app = self::downloadApp($app);
 			} else {
-				$app = OC_Installer::installShippedApp($app);
+				$app = Installer::installShippedApp($app);
 			}
 		} else {
 			// Maybe the app is already installed - compare the version in this
diff --git a/lib/private/legacy/installer.php b/lib/private/legacy/installer.php
index 2bf95f3319..cc80423b7d 100644
--- a/lib/private/legacy/installer.php
+++ b/lib/private/legacy/installer.php
@@ -37,15 +37,19 @@
  *
  */
 
+namespace OC;
+
 use OC\App\CodeChecker\CodeChecker;
 use OC\App\CodeChecker\EmptyCheck;
 use OC\App\CodeChecker\PrivateCheck;
-use OC\OCSClient;
+use OC_App;
+use OC_DB;
+use OC_Helper;
 
 /**
  * This class provides the functionality needed to install, update and remove plugins/apps
  */
-class OC_Installer {
+class Installer {
 
 	/**
 	 *
@@ -138,15 +142,15 @@ class OC_Installer {
 		OC_App::executeRepairSteps($appId, $appData['repair-steps']['install']);
 
 		//set the installed version
-		\OC::$server->getAppConfig()->setValue($info['id'], 'installed_version', OC_App::getAppVersion($info['id']));
-		\OC::$server->getAppConfig()->setValue($info['id'], 'enabled', 'no');
+		\OC::$server->getConfig()->setAppValue($info['id'], 'installed_version', OC_App::getAppVersion($info['id']));
+		\OC::$server->getConfig()->setAppValue($info['id'], 'enabled', 'no');
 
-		//set remote/public handelers
+		//set remote/public handlers
 		foreach($info['remote'] as $name=>$path) {
-			OCP\Config::setAppValue('core', 'remote_'.$name, $info['id'].'/'.$path);
+			\OC::$server->getConfig()->setAppValue('core', 'remote_'.$name, $info['id'].'/'.$path);
 		}
 		foreach($info['public'] as $name=>$path) {
-			OCP\Config::setAppValue('core', 'public_'.$name, $info['id'].'/'.$path);
+			\OC::$server->getConfig()->setAppValue('core', 'public_'.$name, $info['id'].'/'.$path);
 		}
 
 		OC_App::setAppTypes($info['id']);
@@ -161,15 +165,15 @@ class OC_Installer {
 	 *
 	 * Checks whether or not an app is installed, i.e. registered in apps table.
 	 */
-	public static function isInstalled( $app ) {
-		return (\OC::$server->getAppConfig()->getValue($app, "installed_version") !== null);
+	public static function 	isInstalled( $app ) {
+		return (\OC::$server->getConfig()->getAppValue($app, "installed_version", null) !== null);
 	}
 
 	/**
 	 * @brief Update an application
 	 * @param array $info
 	 * @param bool $isShipped
-	 * @throws Exception
+	 * @throws \Exception
 	 * @return bool
 	 *
 	 * This function could work like described below, but currently it disables and then
@@ -232,7 +236,7 @@ class OC_Installer {
 	 *
 	 * @param integer $ocsId
 	 * @return bool
-	 * @throws Exception
+	 * @throws \Exception
 	 */
 	public static function updateAppByOCSId($ocsId) {
 		$ocsClient = new OCSClient(
@@ -260,7 +264,7 @@ class OC_Installer {
 	/**
 	 * @param array $data
 	 * @return array
-	 * @throws Exception
+	 * @throws \Exception
 	 */
 	public static function downloadApp($data = array()) {
 		$l = \OC::$server->getL10N('lib');
@@ -296,7 +300,7 @@ class OC_Installer {
 		$extractDir = \OC::$server->getTempManager()->getTemporaryFolder();
 		OC_Helper::rmdirr($extractDir);
 		mkdir($extractDir);
-		if($archive=OC_Archive::open($path)) {
+		if($archive=\OC_Archive::open($path)) {
 			$archive->extract($extractDir);
 		} else {
 			OC_Helper::rmdirr($extractDir);
@@ -378,7 +382,7 @@ class OC_Installer {
 		}
 
 		// check the code for not allowed calls
-		if(!$isShipped && !OC_Installer::checkCode($extractDir)) {
+		if(!$isShipped && !Installer::checkCode($extractDir)) {
 			OC_Helper::rmdirr($extractDir);
 			throw new \Exception($l->t("App can't be installed because of not allowed code in the App"));
 		}
@@ -460,7 +464,7 @@ class OC_Installer {
 	 * The function will check if the app is already downloaded in the apps repository
 	 */
 	public static function isDownloaded( $name ) {
-		foreach(OC::$APPSROOTS as $dir) {
+		foreach(\OC::$APPSROOTS as $dir) {
 			$dirToTest  = $dir['path'];
 			$dirToTest .= '/';
 			$dirToTest .= $name;
@@ -494,7 +498,7 @@ class OC_Installer {
 			OC_App::executeRepairSteps($appId, $appData['repair-steps']['uninstall']);
 		}
 
-		if(OC_Installer::isDownloaded( $appId )) {
+		if(Installer::isDownloaded( $appId )) {
 			$appDir=OC_App::getInstallPath() . '/' . $appId;
 			OC_Helper::rmdirr($appDir);
 
@@ -517,25 +521,25 @@ class OC_Installer {
 	 */
 	public static function installShippedApps($softErrors = false) {
 		$errors = [];
-		foreach(OC::$APPSROOTS as $app_dir) {
+		foreach(\OC::$APPSROOTS as $app_dir) {
 			if($dir = opendir( $app_dir['path'] )) {
 				while( false !== ( $filename = readdir( $dir ))) {
 					if( substr( $filename, 0, 1 ) != '.' and is_dir($app_dir['path']."/$filename") ) {
 						if( file_exists( $app_dir['path']."/$filename/appinfo/info.xml" )) {
-							if(!OC_Installer::isInstalled($filename)) {
+							if(!Installer::isInstalled($filename)) {
 								$info=OC_App::getAppInfo($filename);
 								$enabled = isset($info['default_enable']);
 								if (($enabled || in_array($filename, \OC::$server->getAppManager()->getAlwaysEnabledApps()))
 									  && \OC::$server->getConfig()->getAppValue($filename, 'enabled') !== 'no') {
 									if ($softErrors) {
 										try {
-											OC_Installer::installShippedApp($filename);
+											Installer::installShippedApp($filename);
 										} catch (\Doctrine\DBAL\Exception\TableExistsException $e) {
 											$errors[$filename] = $e;
 											continue;
 										}
 									} else {
-										OC_Installer::installShippedApp($filename);
+										Installer::installShippedApp($filename);
 									}
 									\OC::$server->getConfig()->setAppValue($filename, 'enabled', 'yes');
 								}
diff --git a/settings/ajax/updateapp.php b/settings/ajax/updateapp.php
index 8521914884..7ac32468fe 100644
--- a/settings/ajax/updateapp.php
+++ b/settings/ajax/updateapp.php
@@ -50,7 +50,7 @@ $appId = OC_App::cleanAppId($appId);
 $config = \OC::$server->getConfig();
 $config->setSystemValue('maintenance', true);
 try {
-	$result = OC_Installer::updateAppByOCSId($appId);
+	$result = \OC\Installer::updateAppByOCSId($appId);
 	$config->setSystemValue('maintenance', false);
 } catch(Exception $ex) {
 	$config->setSystemValue('maintenance', false);
diff --git a/tests/lib/installer.php b/tests/lib/InstallerTest.php
similarity index 74%
rename from tests/lib/installer.php
rename to tests/lib/InstallerTest.php
index ca210ba31e..e1c17b841a 100644
--- a/tests/lib/installer.php
+++ b/tests/lib/InstallerTest.php
@@ -6,7 +6,12 @@
  * See the COPYING-README file.
  */
 
-class Test_Installer extends \Test\TestCase {
+namespace Test;
+
+
+use OC\Installer;
+
+class InstallerTest extends TestCase {
 
 	private static $appid = 'testapp';
 	private $appstore;
@@ -17,11 +22,11 @@ class Test_Installer extends \Test\TestCase {
 		$config = \OC::$server->getConfig();
 		$this->appstore = $config->setSystemValue('appstoreenabled', true);
 		$config->setSystemValue('appstoreenabled', true);
-		OC_Installer::removeApp(self::$appid);
+		Installer::removeApp(self::$appid);
 	}
 
 	protected function tearDown() {
-		OC_Installer::removeApp(self::$appid);
+		Installer::removeApp(self::$appid);
 		\OC::$server->getConfig()->setSystemValue('appstoreenabled', $this->appstore);
 
 		parent::tearDown();
@@ -33,7 +38,7 @@ class Test_Installer extends \Test\TestCase {
 		$pathOfTestApp .= 'testapp.zip';
 
 		$tmp = \OC::$server->getTempManager()->getTemporaryFile('.zip');
-		OC_Helper::copyr($pathOfTestApp, $tmp);
+		\OC_Helper::copyr($pathOfTestApp, $tmp);
 
 		$data = array(
 			'path' => $tmp,
@@ -44,8 +49,8 @@ class Test_Installer extends \Test\TestCase {
 			]
 		);
 
-		OC_Installer::installApp($data);
-		$isInstalled = OC_Installer::isInstalled(self::$appid);
+		Installer::installApp($data);
+		$isInstalled = Installer::isInstalled(self::$appid);
 
 		$this->assertTrue($isInstalled);
 	}
@@ -56,7 +61,7 @@ class Test_Installer extends \Test\TestCase {
 		$pathOfOldTestApp .= 'testapp.zip';
 
 		$oldTmp = \OC::$server->getTempManager()->getTemporaryFile('.zip');
-		OC_Helper::copyr($pathOfOldTestApp, $oldTmp);
+		\OC_Helper::copyr($pathOfOldTestApp, $oldTmp);
 
 		$oldData = array(
 			'path' => $oldTmp,
@@ -72,7 +77,7 @@ class Test_Installer extends \Test\TestCase {
 		$pathOfNewTestApp .= 'testapp2.zip';
 
 		$newTmp = \OC::$server->getTempManager()->getTemporaryFile('.zip');
-		OC_Helper::copyr($pathOfNewTestApp, $newTmp);
+		\OC_Helper::copyr($pathOfNewTestApp, $newTmp);
 
 		$newData = array(
 			'path' => $newTmp,
@@ -83,11 +88,11 @@ class Test_Installer extends \Test\TestCase {
 			]
 		);
 
-		OC_Installer::installApp($oldData);
-		$oldVersionNumber = OC_App::getAppVersion(self::$appid);
+		Installer::installApp($oldData);
+		$oldVersionNumber = \OC_App::getAppVersion(self::$appid);
 
-		OC_Installer::updateApp($newData);
-		$newVersionNumber = OC_App::getAppVersion(self::$appid);
+		Installer::updateApp($newData);
+		$newVersionNumber = \OC_App::getAppVersion(self::$appid);
 
 		$this->assertNotEquals($oldVersionNumber, $newVersionNumber);
 	}