I can kind of believe this is true. Since I know if someone formats a drive, I can get bits of the data back with strings /dev/sda but if they dd it with zero

I can kind of believe this is true. Since I know if someone formats a drive, I can get bits of the data back with strings /dev/sda but if they dd it with zeros, I can't do that. I suspect most/all data recovery firms will only deal with the 95%* of easier cases - which involve them basically running some software and not opening the drive. If they are bit better they might attempt the 4.9%* of cases where they have to replace/fix/bypass the drive's firmware. They write off the 0.1%* with dd style problems because they would cost too much for the customer and would need a better class of staff (recovery typically only costs a three-digit sum) That said it depends, how secure you need your data to be. I think given a budget of $100k (if not less) for one drive this could be possible (i.e. a government, competitor company). For example you could employ people from the company who makes the drives, reprogram the firmware to read the weak magnetic data etc. * percentages made up, to illustrate the point.