If you install opencart 3.x, you will facing the security problem.
After you have install the opencart 3.x and go to backend, you will notify by a security warning.
It will require you to move your storage folder. If you want to move it manually, you may follow below steps.
1. There are 2 files you should change, please download these 2 files and open it with notepad or dreamweaver.
admin/config.php
config.php
2. These sample is assume you will move the folder to www.yourdomain.com/storage.
Find this code in 2 files:
define('DIR_STORAGE', DIR_SYSTEM . 'storage/');
Change to:
define('DIR_STORAGE', '/home/www/yourdomain.com/storage/');
save.
3. Upload to your website’s folder.
4. Go to your website’s folder, delete the exist storage folder.
5. move yourdomain.com/system/storage folder to yourdomain.com/
6. then you may go back to your domain backend and you will find that the problem is solved.