We know that home PCs are often hijacked to send spam. We know they are often pilfered for personal data. Did you also know home PCs are sometimes used as "middle-men" or proxies to help hide the source of an attack?
It works like this: An attacker decides on a target network or PC to hack and at the same time, wants to cover their tracks. To cover there tracks, they must connect through multiple systems before attacking the target — a technique often called "puddle-jumping". This makes tracking them down very difficult — even if they target company or person determines the computer that attacked them, that system is quite often just one in a string of systems leading back to the attacker.
This posting explains how this system works and provides a great diagram showing how an attacker might bounce through different systems and networks before reaching the target. To actually find and apprehend the attacker, the investigator would have to obtain logs and information from each one of the machines involved in the attack — something very difficult, even for law enforcement using subpoenas and other legal tools.
What’s the best plan? Obviously, securing your own system so you don’t become part of this "attack proxy" is the best idea.