A story in USA Today details how easily a Windows machine connected to the Internet (e.g. via DSL or cable modem) can be hijacked. Macintosh and Linux machines were also tested, but it was found that the numerous security holes in Windows made it more difficult to keep the machine secure.
Properly configured firewalls were considered essential, and on any of the machines running firewalls, there were no compromises. The Windows machines that were not running firewalls were broached "within minutes," with over three hundred attacks per hour noted on all the machines.