Our colleagues from the Linux team blogged about it last month, but it's worth repeating:
The latest version of our Emergency Rescue CD is available.
It's a bootable Linux CD that can scan Windows hard drives (NTFS and FAT) as well attached USB drives.
If the computer has an Internet connection, the virus definition databases are updated automatically. If an Internet connection isn't available, the definition databases can be manually updated using a USB drive.
It's an excellent support tool. It's also one of the best ways to scan for MBR rootkit infections.
You can download it from here and read more details from the Linux team's post.