Malware is defined as "short for malicious software, is any software used to disrupt computer operation, gather sensitive information, or gain access to private computer systems. It can appear in the form of code, scripts, active content, and other software. 'Malware' is a general term used to refer to a variety of forms of hostile or intrusive software." (http://en.wikipedia.org/wiki/Malware)
I define it more broadly and simply as "any unwanted applications that are running when you didn't specifically request them to run".
This runs the gamut of annoying, to truly malicious.
If you want to REALLY get rid of malware, you cannot boot within the Operating System (OS) that is infected and expect it to heal itself. The reasons for this are many, but most notably some malware - like rootkits - can install themselves so low-level that they start before the OS does. Therefore no program, running under the OS can even see the files, let alone disinfect or delete them.
So in order to remove files like this the drive has to be working on externally from the infected system. The good news is, there is a way to "externally" work on your own hard disk drive (HDD), using your own PC's hardware, by booting solely off of a CD-ROM, and never booting from the infected HDD.
To do this, you need to download a Rescue Disc Image in the ISO format. Then use a program, such as Infrarecorder, to burn the ISO file to a bootable CD-ROM (or DVD-ROM).
Make sure in the BIOS of your PC that you can boot from your CD / DVD drive. I like to set the boot order to: [1] CD / DVD Drive, [2] Removable / USB Drive, then finally [3] HDD.
If your PC is an untrabook or for some other reason does not have a CD / DVD drive, you can try making a USB Rescue Drive or you can get one of these inexpensive USB optical drives which any good tech outta have in their 'tool box'.
Here's where to get the ISOs I recommend:
AVG Rescue Disc (AVGRD):
http://www.avg.com/us-en/avg-rescue-cd
Kaspersky Rescue Disk (KAVRD):
http://support.kaspersky.com/us/viruses/rescuedisk/
While you're at it, make sure your drive integrity is good - purchase a copy of SpinRite - and run it. It really can make a difference, and will give you early warning of a HDD that's heading south.
Happy Hunting!
-J
