HP admitted at the beginning of this month, that thanks to a loophole, it is selling more copies of the XP operating system than Vista.

And the very same loophole is allowing all of the computer manufacturers - including Dell - to continue to sell the now supposedly defunct operating system.

Well it seems an astonishing third of all of those computer buyers who opt for a Vista PC, are, in fact, then "downgrading" to XP.

The research comes from Devil Mountain Software, which claims that almost 35% of the 3000-plus PCs it examined had been downgraded from Vista to XP.

"Either these machines were downgraded by [sellers like] Dell or HP, or they were downgraded by the user after they got the machine", said Craig Barth, the chief technology officer of Devil Mountain.

"In any case, these machines are no longer running Vista."

The team at Devil Mountain used data uploaded by PC users into its exo.performance.network but has also partnered with Infoworld magazine.

"The 35% is only an estimate, but it shows a trend within our own user base", Barth added. "People are taking advantage of Vista's downgrade rights."

"Vista's installed base certainly doesn't equal the number of Vista licences [that Microsoft's] sold", Barth said, citing the exo.performance.network data as proof. "We're seeing this a lot in the financial sector."