diff --git a/apps/dav/appinfo/info.xml b/apps/dav/appinfo/info.xml
index 633658674c5..46bbca0b3de 100644
--- a/apps/dav/appinfo/info.xml
+++ b/apps/dav/appinfo/info.xml
@@ -5,7 +5,7 @@
 	<name>WebDAV</name>
 	<summary>WebDAV endpoint</summary>
 	<description>WebDAV endpoint</description>
-	<version>1.9.0</version>
+	<version>1.9.1</version>
 	<licence>agpl</licence>
 	<author>owncloud.org</author>
 	<namespace>DAV</namespace>
@@ -31,6 +31,7 @@
 			<step>OCA\DAV\Migration\CalDAVRemoveEmptyValue</step>
 			<step>OCA\DAV\Migration\BuildCalendarSearchIndex</step>
 			<step>OCA\DAV\Migration\RefreshWebcalJobRegistrar</step>
+			<step>OCA\DAV\Migration\RemoveClassifiedEventActivity</step>
 		</post-migration>
 	</repair-steps>
 
diff --git a/apps/dav/composer/composer/autoload_classmap.php b/apps/dav/composer/composer/autoload_classmap.php
index 537bd72d4ca..539ba5d0533 100644
--- a/apps/dav/composer/composer/autoload_classmap.php
+++ b/apps/dav/composer/composer/autoload_classmap.php
@@ -155,6 +155,7 @@ return array(
     'OCA\\DAV\\Migration\\CalDAVRemoveEmptyValue' => $baseDir . '/../lib/Migration/CalDAVRemoveEmptyValue.php',
     'OCA\\DAV\\Migration\\FixBirthdayCalendarComponent' => $baseDir . '/../lib/Migration/FixBirthdayCalendarComponent.php',
     'OCA\\DAV\\Migration\\RefreshWebcalJobRegistrar' => $baseDir . '/../lib/Migration/RefreshWebcalJobRegistrar.php',
+    'OCA\\DAV\\Migration\\RemoveClassifiedEventActivity' => $baseDir . '/../lib/Migration/RemoveClassifiedEventActivity.php',
     'OCA\\DAV\\Migration\\Version1004Date20170825134824' => $baseDir . '/../lib/Migration/Version1004Date20170825134824.php',
     'OCA\\DAV\\Migration\\Version1004Date20170919104507' => $baseDir . '/../lib/Migration/Version1004Date20170919104507.php',
     'OCA\\DAV\\Migration\\Version1004Date20170924124212' => $baseDir . '/../lib/Migration/Version1004Date20170924124212.php',
diff --git a/apps/dav/composer/composer/autoload_static.php b/apps/dav/composer/composer/autoload_static.php
index d6c5628b191..5a23166b027 100644
--- a/apps/dav/composer/composer/autoload_static.php
+++ b/apps/dav/composer/composer/autoload_static.php
@@ -170,6 +170,7 @@ class ComposerStaticInitDAV
         'OCA\\DAV\\Migration\\CalDAVRemoveEmptyValue' => __DIR__ . '/..' . '/../lib/Migration/CalDAVRemoveEmptyValue.php',
         'OCA\\DAV\\Migration\\FixBirthdayCalendarComponent' => __DIR__ . '/..' . '/../lib/Migration/FixBirthdayCalendarComponent.php',
         'OCA\\DAV\\Migration\\RefreshWebcalJobRegistrar' => __DIR__ . '/..' . '/../lib/Migration/RefreshWebcalJobRegistrar.php',
+        'OCA\\DAV\\Migration\\RemoveClassifiedEventActivity' => __DIR__ . '/..' . '/../lib/Migration/RemoveClassifiedEventActivity.php',
         'OCA\\DAV\\Migration\\Version1004Date20170825134824' => __DIR__ . '/..' . '/../lib/Migration/Version1004Date20170825134824.php',
         'OCA\\DAV\\Migration\\Version1004Date20170919104507' => __DIR__ . '/..' . '/../lib/Migration/Version1004Date20170919104507.php',
         'OCA\\DAV\\Migration\\Version1004Date20170924124212' => __DIR__ . '/..' . '/../lib/Migration/Version1004Date20170924124212.php',
diff --git a/apps/dav/lib/Migration/RemoveClassifiedEventActivity.php b/apps/dav/lib/Migration/RemoveClassifiedEventActivity.php
new file mode 100644
index 00000000000..1f1edf285ac
--- /dev/null
+++ b/apps/dav/lib/Migration/RemoveClassifiedEventActivity.php
@@ -0,0 +1,124 @@
+<?php
+declare(strict_types=1);
+/**
+ * @copyright Copyright (c) 2019 Joas Schilling <coding@schilljs.com>
+ *
+ * @license GNU AGPL version 3 or any later version
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, either version 3 of the
+ * License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+namespace OCA\DAV\Migration;
+
+use OCA\DAV\CalDAV\CalDavBackend;
+use OCP\IDBConnection;
+use OCP\Migration\IOutput;
+use OCP\Migration\IRepairStep;
+
+class RemoveClassifiedEventActivity implements IRepairStep {
+
+	/** @var IDBConnection */
+	private $connection;
+
+	public function __construct(IDBConnection $connection) {
+		$this->connection = $connection;
+	}
+
+	/**
+	 * @inheritdoc
+	 */
+	public function getName() {
+		return 'Remove activity entries of private events';
+	}
+
+	/**
+	 * @inheritdoc
+	 */
+	public function run(IOutput $output) {
+		if (!$this->connection->tableExists('activity')) {
+			return;
+		}
+
+		$deletedEvents = $this->removePrivateEventActivity();
+		$deletedEvents += $this->removeConfidentialUncensoredEventActivity();
+
+		$output->info("Removed $deletedEvents activity entries");
+	}
+
+	protected function removePrivateEventActivity(): int {
+		$deletedEvents = 0;
+
+		$delete = $this->connection->getQueryBuilder();
+		$delete->delete('activity')
+			->where($delete->expr()->neq('affecteduser', $delete->createParameter('owner')))
+			->andWhere($delete->expr()->eq('object_type', $delete->createParameter('type')))
+			->andWhere($delete->expr()->eq('object_id', $delete->createParameter('calendar_id')))
+			->andWhere($delete->expr()->like('subjectparams', $delete->createParameter('event_uid')));
+
+		$query = $this->connection->getQueryBuilder();
+		$query->select('c.principaluri', 'o.calendarid', 'o.uid')
+			->from('calendarobjects', 'o')
+			->leftJoin('o', 'calendars', 'c', $query->expr()->eq('c.id', 'o.calendarid'))
+			->where($query->expr()->eq('o.classification', $query->createNamedParameter(CalDavBackend::CLASSIFICATION_PRIVATE)));
+		$result = $query->execute();
+
+		while ($row = $result->fetch()) {
+			$delete->setParameter('owner', $this->getPrincipal($row['principaluri']))
+				->setParameter('type', 'calendar')
+				->setParameter('calendar_id', $row['calendarid'])
+				->setParameter('event_uid', '%' . $this->connection->escapeLikeParameter('{"id":"' . $row['uid'] . '"') . '%');
+			$deletedEvents += $delete->execute();
+		}
+		$result->closeCursor();
+
+		return $deletedEvents;
+	}
+
+	protected function removeConfidentialUncensoredEventActivity(): int {
+		$deletedEvents = 0;
+
+		$delete = $this->connection->getQueryBuilder();
+		$delete->delete('activity')
+			->where($delete->expr()->neq('affecteduser', $delete->createParameter('owner')))
+			->andWhere($delete->expr()->eq('object_type', $delete->createParameter('type')))
+			->andWhere($delete->expr()->eq('object_id', $delete->createParameter('calendar_id')))
+			->andWhere($delete->expr()->like('subjectparams', $delete->createParameter('event_uid')))
+			->andWhere($delete->expr()->notLike('subjectparams', $delete->createParameter('filtered_name')));
+
+		$query = $this->connection->getQueryBuilder();
+		$query->select('c.principaluri', 'o.calendarid', 'o.uid')
+			->from('calendarobjects', 'o')
+			->leftJoin('o', 'calendars', 'c', $query->expr()->eq('c.id', 'o.calendarid'))
+			->where($query->expr()->eq('o.classification', $query->createNamedParameter(CalDavBackend::CLASSIFICATION_CONFIDENTIAL)));
+		$result = $query->execute();
+
+		while ($row = $result->fetch()) {
+			$delete->setParameter('owner', $this->getPrincipal($row['principaluri']))
+				->setParameter('type', 'calendar')
+				->setParameter('calendar_id', $row['calendarid'])
+				->setParameter('event_uid', '%' . $this->connection->escapeLikeParameter('{"id":"' . $row['uid'] . '"') . '%')
+				->setParameter('filtered_name', '%' . $this->connection->escapeLikeParameter('{"id":"' . $row['uid'] . '","name":"Busy"') . '%');
+			$deletedEvents += $delete->execute();
+		}
+		$result->closeCursor();
+
+		return $deletedEvents;
+	}
+
+	protected function getPrincipal(string $principalUri): string {
+		$uri = explode('/', $principalUri);
+		return $uri[2];
+	}
+}