diff --git a/source/packages/com_mokosuitebackup/config.xml b/source/packages/com_mokosuitebackup/config.xml
index f0ce6bda..bd73a14d 100644
--- a/source/packages/com_mokosuitebackup/config.xml
+++ b/source/packages/com_mokosuitebackup/config.xml
@@ -162,6 +162,17 @@
 			<option value="1">JYES</option>
 			<option value="0">JNO</option>
 		</field>
+		<field
+			name="lock_admin_during_backup"
+			type="radio"
+			label="COM_MOKOJOOMBACKUP_CONFIG_LOCK_ADMIN"
+			description="COM_MOKOJOOMBACKUP_CONFIG_LOCK_ADMIN_DESC"
+			default="1"
+			class="btn-group"
+		>
+			<option value="1">JYES</option>
+			<option value="0">JNO</option>
+		</field>
 	</fieldset>
 
 	<fieldset name="cleanup" label="COM_MOKOJOOMBACKUP_CONFIG_CLEANUP">
diff --git a/source/packages/com_mokosuitebackup/language/en-GB/com_mokosuitebackup.ini b/source/packages/com_mokosuitebackup/language/en-GB/com_mokosuitebackup.ini
index fa663c7f..30d012bd 100644
--- a/source/packages/com_mokosuitebackup/language/en-GB/com_mokosuitebackup.ini
+++ b/source/packages/com_mokosuitebackup/language/en-GB/com_mokosuitebackup.ini
@@ -335,6 +335,8 @@ COM_MOKOJOOMBACKUP_CONFIG_PREUPDATE_AUTO_INTERCEPT="Auto-run on Update click"
 COM_MOKOJOOMBACKUP_CONFIG_PREUPDATE_AUTO_INTERCEPT_DESC="When enabled, clicking the Update button on the Joomla Update or Extensions update page first pops the backup progress modal, runs the pre-update backup, then automatically continues the update. When disabled, a notice with a manual 'Back up now' button is shown instead."
 COM_MOKOJOOMBACKUP_CONFIG_BACKUP_BEFORE_UNINSTALL="Backup Before Extension Uninstall"
 COM_MOKOJOOMBACKUP_CONFIG_BACKUP_BEFORE_UNINSTALL_DESC="Automatically run a full backup before any extension is uninstalled. Uses the default profile. Throttled to once per 10 minutes."
+COM_MOKOJOOMBACKUP_CONFIG_LOCK_ADMIN="Lock admin during backup"
+COM_MOKOJOOMBACKUP_CONFIG_LOCK_ADMIN_DESC="While a backup is actively running, show a \"backup in progress\" screen on all other admin pages until it finishes, so nothing changes mid-backup. The backup screen itself and the login page stay accessible. Auto-releases if a backup stops responding."
 
 ; Full-screen backup progress view (runbackup)
 COM_MOKOJOOMBACKUP_RUNBACKUP_TITLE="Backing Up"
diff --git a/source/packages/com_mokosuitebackup/language/en-US/com_mokosuitebackup.ini b/source/packages/com_mokosuitebackup/language/en-US/com_mokosuitebackup.ini
index 61f2219d..cd24d53b 100644
--- a/source/packages/com_mokosuitebackup/language/en-US/com_mokosuitebackup.ini
+++ b/source/packages/com_mokosuitebackup/language/en-US/com_mokosuitebackup.ini
@@ -57,6 +57,8 @@ COM_MOKOJOOMBACKUP_CONFIG_PREUPDATE_AUTO_INTERCEPT="Auto-run on Update click"
 COM_MOKOJOOMBACKUP_CONFIG_PREUPDATE_AUTO_INTERCEPT_DESC="When enabled, clicking the Update button on the Joomla Update or Extensions update page first pops the backup progress modal, runs the pre-update backup, then automatically continues the update. When disabled, a notice with a manual 'Back up now' button is shown instead."
 COM_MOKOJOOMBACKUP_CONFIG_BACKUP_BEFORE_UNINSTALL="Backup Before Extension Uninstall"
 COM_MOKOJOOMBACKUP_CONFIG_BACKUP_BEFORE_UNINSTALL_DESC="Automatically run a full backup before any extension is uninstalled. Uses the default profile. Throttled to once per 10 minutes."
+COM_MOKOJOOMBACKUP_CONFIG_LOCK_ADMIN="Lock admin during backup"
+COM_MOKOJOOMBACKUP_CONFIG_LOCK_ADMIN_DESC="While a backup is actively running, show a \"backup in progress\" screen on all other admin pages until it finishes, so nothing changes mid-backup. The backup screen itself and the login page stay accessible. Auto-releases if a backup stops responding."
 
 ; Full-screen backup progress view (runbackup)
 COM_MOKOJOOMBACKUP_RUNBACKUP_TITLE="Backing Up"
diff --git a/source/packages/plg_system_mokosuitebackup/language/en-GB/plg_system_mokosuitebackup.ini b/source/packages/plg_system_mokosuitebackup/language/en-GB/plg_system_mokosuitebackup.ini
index 7cc78952..e3085701 100644
--- a/source/packages/plg_system_mokosuitebackup/language/en-GB/plg_system_mokosuitebackup.ini
+++ b/source/packages/plg_system_mokosuitebackup/language/en-GB/plg_system_mokosuitebackup.ini
@@ -15,3 +15,5 @@ PLG_SYSTEM_MOKOJOOMBACKUP_BACKUP_COMPLETE="Backup complete — safe to update."
 PLG_SYSTEM_MOKOJOOMBACKUP_BACKUP_FAILED="Backup failed"
 PLG_SYSTEM_MOKOJOOMBACKUP_BACKUP_STARTING="Starting backup…"
 PLG_SYSTEM_MOKOSUITEBACKUP_UPDATE_RUNNING="Backup complete. The update is now running — please wait and do not close this window…"
+PLG_SYSTEM_MOKOSUITEBACKUP_LOCK_TITLE="Backup in progress"
+PLG_SYSTEM_MOKOSUITEBACKUP_LOCK_MESSAGE="A MokoSuiteBackup backup is currently running in another window. The administrator area is locked until it finishes — this page will refresh automatically. Please do not make changes while the backup runs."
diff --git a/source/packages/plg_system_mokosuitebackup/language/en-US/plg_system_mokosuitebackup.ini b/source/packages/plg_system_mokosuitebackup/language/en-US/plg_system_mokosuitebackup.ini
index 12552aea..2f6c301e 100644
--- a/source/packages/plg_system_mokosuitebackup/language/en-US/plg_system_mokosuitebackup.ini
+++ b/source/packages/plg_system_mokosuitebackup/language/en-US/plg_system_mokosuitebackup.ini
@@ -15,3 +15,5 @@ PLG_SYSTEM_MOKOJOOMBACKUP_BACKUP_COMPLETE="Backup complete — safe to update."
 PLG_SYSTEM_MOKOJOOMBACKUP_BACKUP_FAILED="Backup failed"
 PLG_SYSTEM_MOKOJOOMBACKUP_BACKUP_STARTING="Starting backup…"
 PLG_SYSTEM_MOKOSUITEBACKUP_UPDATE_RUNNING="Backup complete. The update is now running — please wait and do not close this window…"
+PLG_SYSTEM_MOKOSUITEBACKUP_LOCK_TITLE="Backup in progress"
+PLG_SYSTEM_MOKOSUITEBACKUP_LOCK_MESSAGE="A MokoSuiteBackup backup is currently running in another window. The administrator area is locked until it finishes — this page will refresh automatically. Please do not make changes while the backup runs."
diff --git a/source/packages/plg_system_mokosuitebackup/src/Extension/MokoSuiteBackup.php b/source/packages/plg_system_mokosuitebackup/src/Extension/MokoSuiteBackup.php
index ea4626e1..c6f869da 100644
--- a/source/packages/plg_system_mokosuitebackup/src/Extension/MokoSuiteBackup.php
+++ b/source/packages/plg_system_mokosuitebackup/src/Extension/MokoSuiteBackup.php
@@ -133,6 +133,10 @@ final class MokoSuiteBackup extends CMSPlugin implements SubscriberInterface
 			return;
 		}
 
+		// While a backup is actively running, lock the admin UI so no other
+		// window/page can navigate or change anything mid-backup. May close().
+		$this->maybeLockAdminDuringBackup();
+
 		// Pre-update: send Joomla core-update installs through the full-screen
 		// backup page BEFORE the update runs (may not return from here).
 		$this->maybeRedirectForUpdate();
@@ -155,6 +159,97 @@ final class MokoSuiteBackup extends CMSPlugin implements SubscriberInterface
 		$this->cleanupOldSnapshots();
 	}
 
+	/**
+	 * Detect whether a stepped backup is actively running right now.
+	 *
+	 * The stepped-backup engine rewrites its session JSON file
+	 * (JPATH_ROOT/tmp/mokosuitebackup-sessions/mb_*.json) on every step and
+	 * deletes it on completion, so a file whose mtime is within the last ~45s
+	 * is a reliable, cross-session heartbeat. A crashed/abandoned backup goes
+	 * stale and stops locking on its own — the admin is never permanently locked.
+	 */
+	private function backupIsActive(): bool
+	{
+		$dir = JPATH_ROOT . '/tmp/mokosuitebackup-sessions';
+
+		if (!is_dir($dir)) {
+			return false;
+		}
+
+		$cutoff = time() - 45;
+
+		foreach (glob($dir . '/mb_*.json') ?: [] as $file) {
+			if (@filemtime($file) >= $cutoff) {
+				return true;
+			}
+		}
+
+		return false;
+	}
+
+	/**
+	 * While a backup is actively running, lock the admin UI: every admin page
+	 * load (except the full-screen backup screen and the login/logout page)
+	 * gets a "backup in progress" interstitial that auto-refreshes, so no other
+	 * window can navigate or change anything mid-backup. Gated by the
+	 * lock_admin_during_backup option; auto-released when the backup ends.
+	 */
+	private function maybeLockAdminDuringBackup(): void
+	{
+		if (!(int) ComponentHelper::getParams('com_mokosuitebackup')->get('lock_admin_during_backup', 1)) {
+			return;
+		}
+
+		$app    = $this->getApplication();
+		$input  = $app->getInput();
+		$option = $input->getCmd('option', '');
+		$view   = $input->getCmd('view', '');
+
+		// Never lock the full-screen backup screen (it IS the backup) nor login/logout.
+		if (($option === 'com_mokosuitebackup' && $view === 'runbackup') || $option === 'com_login') {
+			return;
+		}
+
+		if (!$this->backupIsActive()) {
+			return;
+		}
+
+		$this->renderBackupLockPage();
+		$app->close();
+	}
+
+	/**
+	 * Emit a self-contained "backup in progress" interstitial that refreshes
+	 * itself (meta refresh) until the backup finishes and the lock releases.
+	 */
+	private function renderBackupLockPage(): void
+	{
+		$app     = $this->getApplication();
+		$title   = Text::_('PLG_SYSTEM_MOKOSUITEBACKUP_LOCK_TITLE');
+		$message = Text::_('PLG_SYSTEM_MOKOSUITEBACKUP_LOCK_MESSAGE');
+		$t       = htmlspecialchars($title, ENT_QUOTES, 'UTF-8');
+		$m       = htmlspecialchars($message, ENT_QUOTES, 'UTF-8');
+
+		$html = '<!doctype html><html lang="en"><head><meta charset="utf-8">'
+			. '<meta name="viewport" content="width=device-width, initial-scale=1">'
+			. '<meta http-equiv="refresh" content="8">'
+			. '<title>' . $t . '</title><style>'
+			. 'html,body{height:100%;margin:0}'
+			. 'body{background:#000;color:#fff;font-family:system-ui,-apple-system,"Segoe UI",Roboto,sans-serif;'
+			. 'display:flex;align-items:center;justify-content:center;text-align:center}'
+			. '.w{max-width:34rem;padding:2rem}'
+			. '.s{width:3rem;height:3rem;margin:0 auto 1.5rem;border:.35rem solid rgba(255,255,255,.2);'
+			. 'border-top-color:#fff;border-radius:50%;animation:sp 1s linear infinite}'
+			. 'h1{font-size:1.5rem;margin:.5rem 0}p{opacity:.85;line-height:1.55}'
+			. '@keyframes sp{to{transform:rotate(360deg)}}'
+			. '</style></head><body><div class="w"><div class="s"></div>'
+			. '<h1>' . $t . '</h1><p>' . $m . '</p></div></body></html>';
+
+		$app->setHeader('Content-Type', 'text/html; charset=utf-8', true);
+		$app->sendHeaders();
+		echo $html;
+	}
+
 	/**
 	 * Inject the client-side interceptor on the Extensions → Update and
 	 * Extensions → Manage pages, so an EXTENSION update / uninstall also runs