No matter how good your precautions, malware can still infect your computer.
If you suspect an infection but your antivirus program tells you otherwise, take Windows out of the calculation and run your AV in a non-Windows environment where the infection can’t hide.
Use Linux to run antivirus software on a PC
Malware can be extremely clever. Infections can block your AV app from doing its job properly; it might even defeat supplementary malware scanners. But malware that infects Windows is specific to that OS. It no longer works and can’t hide as easily from another operating system.
There are plenty of good, free malware scanners that run in other environments — many of them Linux-based. And the good news is, you don’t have to know anything about Linux to use them. Simply boot the non-Windows OS, and the scanner of your choice pops up.
Choose the best media for your AV system
Virtually all non-Windows AV tools are designed to boot from CDs. You can also put them onto a bootable flash drive, but that generally takes more work. And it might be worth the extra effort. Not all PCs have a working optical drive, but they all have a USB port. You can carry a flash drive in your pocket and, when you’re through using it as an AV tool, use it for something else.
But since these programs are designed to be put onto optical discs, let’s start there.
For bootable CDs, you need .iso-file support
You can’t copy AV and system files to a CD and expect them to boot a PC. You have to burn an .iso image (Wikipedia definition) onto the disc. Think of .iso files as downloadable CDs. Many AV applications can be downloaded as bootable .iso files.