Abstract: A system and method for creating computer system backups, particularly well-suited for performing backups of virtual machines. The method starts by reading the current state of the machine, in blocks of a constant size, and creates a “FULL” index of block numbers and a hash value associated with the data within that block, while at the same time creating a FULL backup of the machine (the FULL backup then stored at an off-site target location). Once the FULL index map is defined, subsequent DELTA backups are created by reading the current state of the device in the same block fashion and generating updated hash values for each data block. The newly-generated hash values are compared against the values stored in the FULL index map. If the hash numbers for a particular block do not match, this is an indication that the data within that block has changed since the last FULL backup was created.