security
Security should be one of your primary concerns in evaluating online backup solutions. There are various aspects of security that you should be concerned about.
encryption
Many backup solutions actually encrypt the data before they transport it off of your computer. The data should remain encrypted while it is stored on the backup provider’s servers. This ensures that the data is still unreadable even if the data center is compromised. Of course, if a hacker is able to retrieve your data and the encryption keys then they would have complete access to your data.
The most secure option would be for only you to control your encryption keys. The danger with this is that if you lost the key then your data would be useless to you. Some backup providers that offer this option discourage it so that you don’t get locked out of your data if you do forget the password/pass phrase that was used to generate the key. We recommend that you manage your own key and pick a password/pass phrase that you won’t forget. If you think you might forget it you should store it somewhere safe (possibly a safe deposit box).
transport
When transporting the data you want to ensure that it gets to the proper destination. Look for providers that use SSL which ensures that the destination is indeed who you think it is. SSL also provides encryption, but this is less important if your files have already been encrypted before transport. Using SSL is still not enough if the provider does not perform sufficiently rigorous checks on the authenticity of the server’s certificates. Here’s an article from Heise Security that further describes some of these issues.