REDMOND, WASHINGTON - Software titan Microsoft is limiting online access to a test version of its eagerly-awaited Windows Vista operating system for fear that downloading it could crash the whole internet.

The beta version has been made available prior to Vista's launch early next year in the hope that testing by amateurs would find bugs that still needed to be fixed.

Microsoft has advised users to order a DVD copy of the software rather than download the massive multi-gigabyte files if they want to take part in the customer preview program.