Hands Off! Personal Computer Privacy

When the World Trade Center buildings collapsed last year, they took with them about $500 million worth of computer equipment, according to financial services company Morgan Stanley.

In spite of elaborate backup systems, some data was housed exclusively in hard drives buried beneath tonnes of rubble, often smashed to bits. Lost? Not necessarily.

Within a month, one computer forensics company alone, Convar Systemme Deutschland, had recovered the data from 39 computers salvaged from the WTC ruins and was beginning work on another 62 using a unique laser tool that took samples from the broken bits to make a "virtual" hard drive and then recreated the original.

It was expensive -- up to $35,000 per hard drive -- but the next time you "erase" something by clicking delete, it might help to remember Convar: once on view, always on recall.

But I'm Just a Home User...

It's not likely that you or anyone else will go to those lengths to recover information from your home computer, but data recovery (snooping) tools are getting more sophisticated -- and cheaper -- all the time.

Convar, for instance, offers a tool called PC Inspector Smart Recovery, that will recover "lost" image or sound files from any computing device -- including external memory storage devices and digital cameras -- for $US139. RTT, another well-regarded data recovery company, offers a home data recovery software suite that will restore entire drives from common types of disaster (or accidental wipes) for $US80.

When you use these utilities, they're tools. When others use them, they're spyware.

What Happens When you Erase Data?

Computer files are just strings of numbers, 1s and 0s. When they're organised into patterns, they can be rendered by a computer as information -- words, pictures, equations, the whole shebang. When even a few number sets at the beginning of a file -- the "pointer" that tells the computer where and what it is -- are randomised, however, the whole file becomes becomes invisible.

Without the protection of its pointer element, the computer treats a deleted file as though it were blank space, and replaces sections of the deleted file with sections of other files until, gradually, all the numbers have been "overwritten". At that point, theoretically, the file is erased.

The process of overwriting deleted files occurs randomly, however, and some files may sit on a hard drive nearly complete for years, while others may vanish in weeks. Any part of a file not completely overwritten can be recovered -- and those fragments are your "invisible" hard drive.

So what's on this invisible hard drive? Copies of everything you've ever looked at online, for one thing -- as well as all the email you've ever sent or received, and every document you've ever read or written using the computer.

That should give you something to think about when you trade your old model in for a new one -- because the chances are good that unless you've taken strong measures to erase your hard drive, everything is still on it, including your financial identity details.

Can I Really Erase a File?

Yes. Maybe.

A growing number of inexpensive software utilities claim they can erase files completely, beyond the reach of even tools like those employed by Convert and its peer organisations -- although recovery technology is advancing rapidly.

Most of the popular file wipe utilities cost under $US25 and work by trying to rewrite a file with meaningless information before it gets deleted.

The US Government has indicated, with a few important caveats, that data handled this way becomes unrecoverable after seven rewrites. Two popular wipe utilities that provide at least seven wipes are mcSanitizer and ShredX. ShredX gives users the option of 35 rewrite passes, and actually tries to wipe places the file might have sequestered away copies of itself as well. You'll want to write over files at least 50 times to get the most complete protection, however.

These tools, and others, can also be used to overwrite -- wipe -- your entire hard drive, but specialty tools, like IBAS ExpertEraser, are far more effective on big jobs.