Does your hard-drive or network-activity light flicker for no apparent reason? While there may be a legitimate reason for it, this could also be a sign that a virus or a hacker’s back-door program (a devious little program that allows secret access without your permission) is running on your computer. You might be donating some of your computer resources to a hacker and be largely unaware of it. Here are some examples of what could be going on if a