Even the best defenses will eventually be defeated and in the case of computers this happens all too often. Even with an antivirus or firewall a system will fall victim, and in some situations malware may render the system incapable of booting or your security solution may be compromised. If this is your case then you might want to consider using any of the three bootable rescue CDs below which have the capability to scan a system for malware and take action without the need to boot the compromised operating system.
I am only reviewing what I’ve used in the past.
BitDefender Recue CD is a solid solution that features automatic signature update(from the Internet) and even starts the scanner by itself. All you have to do is wait for the scanner to finish and then take action. Asides from the scanner itself you can expect other useful utilities like FireFox, Nessus, GtkRecover, and ChkRootkit. You can download BitDefender Rescue CD from http://download.bitdefender.com/rescue_cd/
F-Secure is another antivirus scanner that is nice enough to rename all files containing malware. It’s also capable of automatically updating the definition database. There are no other features just the scanner. You can download F-Secure Rescue Disk from http://www.f-secure.com/en_EMEA/security/security-lab/tools-and-services/rescue-cd/index.html
Kaspersky is another free of charge rescue Disk which can also automatically update its database of known malware. All you have to do is check the drives you wish to scan and hit start scan. In the end you can even get a nice .txt report. You can download Kaspersky Rescue Disk from http://devbuilds.kaspersky-labs.com/devbuilds/RescueDisk/