KillDisk is licensed per concurrent use of the software and for each concurrent disk being erased or wiped, outlined in the EULA. The maximum number of disks erased in parallel corresponds to the number of purchased licenses.
KillDisk Industrial is supplied with a security USB key that
contains number of licenses being purchased (one license is required per slot where HDD/SSD is
plugged into). 
Figure: Security USB key containing licenses
This key must be inserted into any USB slot on the PC before running KillDisk software, otherwise authorization error appears.
For KillDisk Systems manufactured by LSoft Technologies the security chip is integrated into the motherboard. In this case no additional USB key needs to be plugged in.