The Register reports on a test conducted on a number of data erasure products:

The Register: Datawiping doesn't work

The result:

eTesting Labs has run a series of tests of eight commercial available diskwiping products - and only one of them worked properly.
This is Redemtech Data Erasure, from the company which contracted eTesting to run the trials. So the results should be treated with caution. The eight products were run on six variously configured PCs
The message: if you want to erase data ... make sure you overwrite it 50 times ...

Cheers,

BrainStop