Microsoft has issued a warning to people who use Apple's Safari browser on their PCs.
The note reads: "Microsoft is investigating new public reports of a blended threat that allows remote code execution on all supported versions of Windows XP and Windows Vista when Apple’s Safari for Windows has been installed".
Microsoft adds that it is not aware of any threats that have taken advantage of this weakness as yet and promises to "take the appropriate measures to protect its customers".
It adds: "This may include providing a solution through a service pack, the monthly update process, or an out-of-cycle security update, depending on customers needs".
For the meanwhile, however, users are being asked to restrict their use of Apple's Safari browser until the patch is made available.
It adds that customers who have changed the default location where Safari downloads content to the local drive are not being affected by this blended threat.
Apple is not commenting as yet on the problem.