Shadow Man (danger.com)

Welcome to the Jungle
The Internet...a world without rules, without boundaries. Where you can be anyone you want, whoever you aren't. And it's all just a click away...
Pepper Oneida is the type of gilr other girls love to hate. She's five feet two of perky perfection who can steal your boyfriend with the wink of an eye. And that's exactly what she's done to Annie Hanley. But Annie's got a plan. With her PC and some help from her stepbrother Nick, she's going to teach Pepper a lesson.
It starts out as a prank. But then Annie and Nick send the wrong message to the wrong person, and things get serious -- serious as a stone-cold killer.
Different people in different places. The only thing they have in common is a new address on the Internet: danger.com. Where all your fears come true.