The Mac OS ROM file can crash Power Mac G3s, iMacs and new G3 PowerBooks, warns Apple’s Web site.

Information on its Tech Info Library pages warns: "Certain combinations of Apple installers can cause the Mac OS ROM file to be downgraded to an earlier version.

"Because specific Mac OS ROM versions are meant for specific releases of Mac OS, mismatching these components can cause unpredictable behaviour. Depending on the Mac OS version and the ROM version which are mismatched, symptoms can vary, from an unnoticeable difference in operation to a system crash or freeze during start-up."

Apple says the problem stems from the running of older system-software installers over newer installed versions.

Actions such as installing the jigsaw from an earlier system-install disk to a later system, for example, may lead to the problem.