Mozy's default is 448-bit Blowfish encryption. You also have the ability to encrypt your data with your own personally generated 256-bit AES key. 

CAUTION: If you opt to use a personal key, you are responsible for remembering that key. If you lose or forget your personal key, you WILL NOT be able to access your backed up files when they are restored. Mozy does not keep any record of any custom keys used.

The encryption type must be selected during your initial install. After Mozy is finished installing, you will see the Summary window. You can click on the Change Encryption link at the bottom of the window to change it. Select the encryption method you want there. If you choose to use a personal key, enter the key by copying or typing it into the Enter Key field or importing a key file using the Browse button next to the Import Key field. 

NOTE: It is HIGHLY recommended that you either save a copy of that key on a separate external storage device, or print it and store it in a safe location. Click OK when done, or Cancel to return to the summary.