Virus's can get real nasty and make your Operating System unbootable, in such cases the user is left with only two choices either to format and re-install the operating system or to use a bootable anti-virus cleaner for removing the virus infection, obviously the second option is the preferred one, almost all major anti-virus companies provide bootable rescue disk's for removal of such stubborn virus infections, Kaspersky Rescue Disk is one of the best bootable anti-virus rescue disk out there with an fully functional option to download latest anti-virus definitions updates from internet, the free rescue disk GUI is similar to Kaspersky Anti-Virus 2009 allowing users to remove virus's and malware's via a familiar interface without booting into Windows.
If you don't have CD/DVD booting functionality or would prefer USB disk as the bootable medium, here is a simple step-by-step guide for creating bootable Kaspersky Rescue USB Disk:
Creating and using a bootable USB rescue disk is a much faster, easier and smarter approach than a bootable cd/dvd, earlier 
A "Bootable Anti-virus Rescue Disk" is a lifesaver when the computer is unable to boot normally or is unstable to such levels that disinfection is not possible because of virus activity, One of the best free bootable antivirus rescue disk "
