Several members in this thread said tape is secure in the case you take the the tapes out of the library and store them offline. This is correct. The tapes cannot be accessed by an attacker in this scenario.

A tape library can be attacked like any other system that has network connection. I did not hear about attacks up to now, but it is theoretically possible. You can protect them like any other system with user/password, 2FA, network security - separated VLAN, etc.

But in the case e.g. the web interface has a vulnerability the system is attackable, no question. The good point in this scenario is, that the media with your data is separated from the system that reads (and in the worst case deletes) your data.

No other storage I am aware of has such a separation - perhaps libraries with optical media, but this is basically the same as tape. Any other storage is fixed in the storage system...