Which? hammered over 'smash disk' advice

The consumer magazine Which? Computing has come under fire for a claim that the only sure way to destroy data from hard disks is to take a hammer to them.

The magazine reported that it recovered 22,000 'deleted' files from eight computers bought on Ebay and points out that software is freely available to do this.

But the idea of destroying a disk is "silly and misleading", according a charity specialising recycling old computers for use in African schools.

Ida Gaye, communications officer for Computers4Africa, wrote in a letter to PCW that it smacked "of a heady mix of sensationalism and a disturbing lack of research on the part of the Which? team ".

She said data was left on disks because people did not release that simply deleting did not destroy it. "The only thing that is actually changed on the hard drive are the pointers that tell the PC where the data is stored- essentially they go from 'this is where the data is' to 'this space for rent'."

Technically smashing a hard disk was to the only way to destroy data 100 per cent though it would have to be professionally shredded to ensure nothing was readable. But any erase program that overwrites the data would make it practically impossible to recover.

"If an obsessive with access to a supercomputer and an electron microscope had several years to work on reverse engineering pseudo-random number generation algorithms, he could potentially(if everything went perfectly) figure out some of what might have been on the hard drive before the data erase was run. In practical terms, that's never going to happen," Gaye wrote.

She added: "Good secure erase programs are quite easy to find on the internet and many of them are even free to use."

Computers4Africa will collect any unwanted computer less than five years old – and will overwrite any data on the hard disk for you.