Dusseldorf, Germany  - The loss of accidentally deleted computer files can be a catastrophe. Yet "deleted" files are not always really gone from your computer. In many cases they can still be recovered, even if no backup was ever created. An attempt at using special data recovery software to fix the problem is usually a good, first step.

A study by the data recovery company Kroll Ontrack shows that defective hardware is responsible for more than half the cases involving data loss.

"One in four is attributable to user error, though," explains Stephanie Hennig from Kroll Ontrack. That includes the accidental deletion of files.

Still, not all hope is lost when it comes to retrieving deleted files. During a standard deletion, the OS simply frees up the files for overwriting.

"It's like a book where the table of contents has been partially removed. It's harder to find the pages, but it's possible," explains Markus Mizgalski from Dusseldorf-based PC Pr@xis magazine.

Data recovery programs rummage through this table of contents for the file system or they attempt to recreate the complete files through the snippets left over on the hard drive. Some programs work better than others for this task. A recent test by PC Pr@xis showed that cost-free software is only partially helpful. The freeware titles tested by the magazine quickly reached their limits, or were difficult to use.

The best grades went to R-Studio Datenrettung 4, available for around 80 dollars. Just behind it in the rankings was O&O DiskRecovery 4, also costing around 80 dollars. Both programs recognize hundreds of file formats, provide a quick search version as well as an advanced version for tricky cases, and can be used as a boot disk for recovery attempts where the OS refuses to load up again. While complex, R-Studio offers occasional users several bonus features: It works with several operating systems and can create an exact copy of the affected storage media - in the event that the failed rescue attempt only deepens the damage.

The freeware alternatives PC Inspector File Recovery and Recuva are significantly less powerful for recovering files accidentally deleted from the Windows recycling bin. Users of Windows tuning programs like TuneUp Utilities or Tvista may not need to buy anything else at all. Data recovery tools are often integrated into those packages.

It's a good idea to test the commercial programs before buying them. In general software publishers offer demo versions for precisely this purpose. "Try to recover ZIP archive data or very large email databases in pst format and you'll quickly separate the wheat from the chaff," says Robert Globisch from computeruniverse. net, an online mail-order catalogue.

There are a few tips to improve the chances of successful recovery. The key one is to immediately stop working on the affected hard drive or storage card once you realize that a file has been lost. That also means no installation of recovery tools not already on the drive as you risk overwriting the very data you want to save.

INFO BOX: Professional data recovery is expensive =

Those who manage to recover their lost documents, photos or media files using software are lucky.

"If the issue is a physical defect in the hardware, the recovery process is more complex and software is no longer an option," explains Stephanie Hennig from Kroll Ontrack, a company specialising in both data recovery software and services. The only option at that point is a trip to the data recovery lab, where the last data is restored manually bit by bit. That can cost anywhere from several hundred to several thousand dollars. (dpa)