Revelations about a hard drive purchased on eBay – which reportedly contained the launch procedures for a US military air defence system - is extremely worrying.

"This is obviously a serious lapse of security procedures for the agency concerned, but the worrying aspect about the incident is that it may not be a one-off. US government agencies - and, indeed, all government agencies worldwide - should have a policy of crushing hard drives once they have been removed from office PCs," said Michael Callahan, Credant's senior vice president.

"But this isn't a one-off situation - if we go back to April 2006, there was the well-publicised incident of a flash drive with US spy data being sold in an Afghan bazaar for just $40. The ensuing investigation into that incident revealed the fact that the data had been downloaded from an unencrypted hard drive," he added.

And the lack of encryption - rather than a lack of enforced policies on disposal of old drives - is the root cause of this latest security incident, he says.

If the data on the PC used in Afghanistan in 2006 had been encrypted, as had the data on the drive reportedly sold on eBay, then the ensuing press embarrassment for the US military would not have happened.

It is, Callahan explained, all very well having a security policy in place for the disposal of unwanted hard drives and other PC components in government agencies, but enforcing such policies is a difficult task.

Difficult, not impossible. And, says Callahan, if government agencies also encrypt all critical and private data on their networks - whether in transit or at rest, as is the case with hard drive storage systems - then this acts as a fail-safe backup for security policy failures.

"I suspect that the investigation by BT's security research centre and a number of international universities will reveal other serious security failures with hard drives," he said.

"The bottom line, as this incident - and the Afghan $40 bazaar sale - clearly proves, is that government IT security procedures, policies and enforcement systems need to be multi-layered and multi-faceted, with encryption forming the mainstay of such protection," he added.