Further details have emerged on the background to Apple's recent news of irregularities in the way it grants share options.

The San Francisco Chronicle reports that the alleged impropriety affected stock granted to 14 current and former officers of the company on 17 dates between 1993 and 2001.

It seems stocks were backdated to a point just after a short drop in Apple's stock value with a pay-off point set just before a substantial rise in value.

Apple has been hit with a lawsuit by angry shareholders. The litigation claims the pattern of these back-dated options grants is so striking that they "could not have been the result of chance".

Apple has launched an internal investigation of these alleged improprieties.