Ubuntu Linux: Since it is not possible to provide a safe patch in a short time, Hyper-Threading has been disabled in the updated kernel packages for now. You can manually enable Hyper-Threading again by passing the kernel parameter "ht=on" at boot. [Quoted from Ubuntu Security Notice USN-131-1.]
I edited /boot/grub/menu.lst to modify this line to add the ht=on. Then I ran "sudo update-grub" to propagate the changes.
# defoptions=quiet splash ht=on