Computers using the speech recognition tool built into Windows Vista are not at risk from malicious commands played in an audio file.

There have been fears voiced by some forum users that a command to delete a file played through the computer speakers would be picked up by the microphone and executed.

A spokesperson for Microsoft said that it would be very unlikely for an attack of this sort to succeed. The speech recognition in Visat is turned off by default and the actions would be plainly visible to the user.

Deleting an important file would also prompt a warning on screen with User Account Control. Warnings of this type cannot be deleted with voice commands and so the attack would fail.

Martin Held from Dragon agreed that there is no realistic threat. For the attack to be successful each command must be recognised exactly, any mistakes and nothing will happen.