Hi, check to see if you have the latest firmware. If not, download and install it. After you update, login and change the admin password to something more secure. Delete the user you are suspicious of, make sure to give all the users you want to keep a more secure password. Go and change the password on your DDNS account. Not sure how you are using your FTP, but lookin to using the SSL/TLS type of connection to access your DNS. I maybe a bit paranoid, but better safe than sorry.