Now it is hard to decide who is in the right here - the person who published the private data on the website (for all you know, the laptop in question could have been damaged in transit) or the seller who is now the talk of the town, whose life is being dissected. There is no way to know. But that is besides the point. The truth is that it is scary to realize that it is next to impossible to delete all the data that one stores on ones storage media without completely destroying it. Because, with the right tools anybody can retrieve even deleted data.
So what can be done to alleviate the situation ? If you are using GNU/Linux or any other UNIX, then you have a tool called
shredwhich can be used to wipe all the data from the hard disk. Here is how it works. Suppose I want to erase all the data on my hard disk, then I boot using a LiveCD like Knoppix and open a shell and type the following command:
# shred -vfz -n 100 /dev/sda
/dev/sdais my whole hard disk. And I am asking
-n100 passes by overwriting the entire hard disk with
-zzeros. And shred program
-fforces the write by changing the permissions wherever necessary.
Another GPLed tool (though not specifically related to Linux) which is quite popular is Darik's Boot and Nuke (DBAN) which also does a great job of securly erasing the data on your hard disk.
Experts in the field of retrieving data can still get some data from a hard disk that has been wiped in the above manner. But at least ordinary folks who buy second hand laptops and computers will find it beyond their means to lay their hands on your data if you have wiped your hard disk this way prior to selling your PC or laptop.