BranoI hate VogonsPremium,MVMReviews:
reply to FirebirdTN
Re: Block web crawlers? Until you've mentioned you're limited to NSA310 I was prepared with some options for you but if you want to stick to the NAS capabilities here are few options to consider:
1) Close the NAS access directly and use SSL or L2TP VPN only (this would remove public access)
2) Get separate FTP server for public access on some cheap server i.e. RaspberryPi ... total cost $50. Install vsftpd, for uploads create one folder witch chown functionality after upload so nobody else can get anything anybody uploads.
For downloads you can make the folders not readable and use direct link to a deeper structure if you know what that is (you can share that with trusted parties only).
Alternatively hack your way into NAS »zyxel.nas-central.org/wiki/SSH_server and install separate FTP server on it.