A short science/speculative fiction story written by Neal Stephenson and published in Wired Magazine- October 1994.
Written in the first person perspective, the narrator is something analogous to a corporate marketing investigator/strategist. His job is to surf something similar to the Internet (a multimedia-rich digital metabase known as "the Spew") and look for anomolous behavior found in users. The main goal of this is to find a previously unexploited market niche, study it and then figure out a way to milk it for all it's worth.
The character is put onto the trail of a particularly odd user profile- one that is almost too normal to be true. He discovers everything about her: where she works, what she buys, what she wears, her tattoo, the music she listens to... everything. He watches her through the security cameras where she works, and in the process, develops a personal fascination with her. When he starts his investigation, it's purely a function of his job, but it somehow turns into something more personal- digital stalking.
The story can be found here:
http://hotwired.lycos.com/collections/connectivity/2.10_spew_pr.html
If you're a fan of Neal Stephenson's work, I would suggest you read this.