This describes a new kind of IT ransom which should be much more professional and profitable.
The attacker manages to access some company’s servers, then encrypts the data in the databases but he modifies the DBs access routines to encrypt/decrypt on the fly all data with his own encryption key. In this way for the company all continues to work. He then waits a few months so that all DB backups are encrypted with his keys and at this point deletes the encryption keys from the company’s systems and asks for a ransom to give it back.Notice that backups are unusable because they too are encrypted with the attacker key.
Obviously, strong IT security procedures should prevent and detect this, from off-line testing of backups to intrusion detection.