Could Malware Render Your PC Unbootable?

I'm not answering a particular reader question this time around, although a recent forum discussion inspired me to write this post. I hear a lot from people with unbootable computers. Maybe they get a Blue Screen of Death (BSoD) with every boot. Or the PC shuts down before Windows finishes loading. Sometimes an error message tells them that there's no operating system on their hard drive, or no hard drive at all. A great many of these users assume that a "virus" is to blame.

This belief is a cultural leftover from the 1990s, when viruses like Leonardo might render your PC unbootable and your data inaccessible. If your PC was infected by Leonardo (which spread via floppy disks), booting on March 6 appeared to wipe everything off of your hard drive (although someone with reasonable technical skills could retrieve most of it).

Back then, writing malware was a cruel hobby. Today, it's an evil profession. The perpetrators want to use your computer to send out spam, take part in distributed denial-of-service (DDoS) attacks, practice extortion, and infect other computers. And as long as they secretly control your PC, they might as well steal your passwords and credit card numbers, too.