MacBook Air purchasers are being warned not to use installation discs from other Macs ito install the operating system.

"The Mac OS X 10.5 installation media that shipped with your MacBook Air is designed for use on this computer only," Apple warns in a technical document posted to its website.

"The installer prevents this software from being installed on other Macintosh computers. Furthermore, other Mac OS X 10.5 installation media should not be used when restoring the system software on your MacBook Air."

The MacBook Air doesn't ship with an included optical drive, so users must install and reinstall their system software by using an external optical drive, or wirelessly using a system called Remote Disc.

Remote Disc lets users wirelessly access discs inserted in the optical drives of other computers on a wireless network, once a piece of software has been installed on the host Mac to support the feature.