There are three main aspects to this subject: the security of the login process; security during data transfer; and the security of the tapes on which the data is ultimately held.
2. The login process
Login to the TSM server is authenticated by a Kerberos-like challenge-response mechanism. This ensures that a unique session key is generated at each login and that passwords are not sent over the network. As such, the TSM login process may be said to be robust.
3. Data transfer
Data is sent to the TSM server by default unencrypted across the network. However, a facility for encrypting data to be backed up is available, using by default 128-bit AES (which, if preferred, can be changed to 256-bit AES for those running TSM 7.1.3 or higher). For information on how to select files for encryption, see our page on TSM encryption. Users may also wish to encrypt sensitive data before backing it up.
4. Data tapes
Your data is copied to three separate tapes. One copy resides in the Tape Robot in the IT Services Machine room. The other two copies are held in locked fireproof safes, one onsite at IT Services, one offsite in locked premises. The data on the tapes is inaccessible without the TSM database. The data on the offsite tapes is encrypted.
A fuller consideration of the security of TSM can be found at http://ist.mit.edu/sites/default/files/services/backup/Security%20Notes%20on%20TSM.pdf.