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Several Windows file-wiping utilities fail to completely wipe some files on Windows NT, Windows 2000 or Windows XP that use NTFS file systems, security researcher Kurt Seifried has discovered.

But computer forensic experts reckon the privacy implications of the advisory are limited, as standard packages, such as Word or Excel, do not make use of the secondary data streams - where file remnants might be left even after data has been securely deleted.

In any case, wiping a disk entirely will destroy such data, as Chris Crute, a forensic investigator at security consultancy Information Risk Management, points out.

In an advisory, security researcher Kurt Seifried details how file wiping utilities, such as PGP Wipe, BCWipe or East-Tec Eraser, fail to implement alternate data stream-wiping properly.

The upshot is this: information contained within the alternate data stream which is attached to a file (such as the thumbnail of an image) or directory remains intact on the hard drive data, when the file or directory is wiped.

It's unlikely that users store sensitive information using alternate data streams (which must be "explicitly created", as the advisory points out). However alternate data streams can provide a location where attack tools, snippets of virus code or the like can reside; and few virus scanners look there for malicious code, unless specifically configured to do so.

This is less bad than it may seem at first because viruses would have to go out of "stealth mode" to cause any harm.

Users can workaround the problem of data inadvertently stored in alternate data streams by using the "wipe free space" feature present in most secure file deletion utilities, but this is time-consuming. Encrypting disc partitions also creates an effective barrier for the recovery of data, though this is not bullet proof.

Vendors of BCWipe and SecureClean are currently updating their software to address the issue, they told Seifried. East-Tec has acknowledged a "possible problem" and is analysing the issue while Network Associates, the developer of PGP Wipe, is yet to respond.

Data annihilation

The efficacy, or otherwise, of file-wiping alternate data streams, is a fairly arcane matter. But data-wiping is an important corporate issue, for security and data protection issues.

The greatest points of weakness are when PCs are sold onto the secondhand market, and when data is stored on easily-stolen laptops.

Two years ago, an obsolete PC sold on by merchant bank Morgan Grenfell Asset Management "contained 108 files relating to Sir Paul McCartney's private cash dealings" was bought secondhand. The PC was released into the second-user market without first being wiped clean of data.

Jon Godfrey, consultant at Technical Asset Management,
the Welwyn Garden City, Herts PC disposal company, in excess of 50 per cent" of corporates fail to destroy sensitive data effectively, because of faulty procedures.

"The biggest problem is technical ignorance. There's a great difference between destruction and deletion of residual data, but most users don't understand this," he said.

Reformatting a disc or even taking a hammer to it will not necessarily prevent the recovery of data.

The one surefire way to achieve this is to overwrite information hundreds of times using software such as Sanitizer, which is operating system-independent. ®

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