Count Zero - William Gibson

They set a Slamhound on Turner's trail in New Delhi, slotted it to his pheromones and the colour of his hair.

When the Maas Biolabs and Hosaka zaibatsus fight it out for world domination, computer cowboys like Turner and Count Zero are just foot soldiers in the great game: useful but ultimately expendable.
When Turner wakes up in Mexico - in a new body with a beautiful woman beside him - his corporate masters let him recuperate for a while, then reactivate his memory for a mission even more dangerous than the one that nearly killed him: the head designer from Maas Biolabs says he wants to defect to Hosaka, and it's Turner's job to deliver him safely.

Count Zero is a rustbelt data-hustler totally unprepared for what comes his way when the designer's defection triggers war in cyberspace. With voodoo gods in the Net and angels in the software, he can only hope that the megacorps and the super-rich have their virtual hands too full to notice the amateur hacker with the black market kit trying desperately to stay alive . . .