Jeffery Deaver. The Blue Nowhere (2001) 426
A sadistic computer hacker, code-named Phate, sets his sights on Silicon
Valley, infiltrating his victims’ computers, invading their lives, and
luring them to their deaths. An imprisoned hacker named Wyatt Gillette
is freed to aid in the investigation, and teams up with old-school homicide
cop Frank Bishop, forming an uneasy alliance in which they must utilize
every ounce of their respective talents to stop Phate.