Even if you take the film's moral lesson at face value, the overkill is discouraging, and not very instructive.
"The whole world wants to watch you and they don't even know you." By the time the killer in Untraceable explains his apparent motive to yet another distraught and doomed victim, you've long since stopped caring. The kid is a remarkably banal psycho killer, obsessed with daddy issues, blaming everyone else for his achy heart, and expending his ostensible genius on diabolical murder contraptions.
The gimmick is the internet, where the killer displays his mad business, inviting users to log on to his site, killwithme.com, where they can not only watch victims suffer from a range of hideous abuses -- bleeding induced by chemicals, burning by sunlamps, dissolving by acid, ho-hum -- but also resist taking responsibility. As the counter ticks off the number of users for each "scene," the cops who are also watching recite the film's mantra-lesson: each click contributes to the death, adding chemicals, voltage, and acid drops.
Into this tedious business steps the most moral cop, an FBI cybercrimes agent located in Portland, where it rains a lot and the killer resides. Confident, righteous, and intuitive, Jennifer Marsh (Diane Lane) lives with her mother (Mary Beth Hurt) and preteen daughter (Perla-Haney Jardine), still smarting from the years-ago death of her PPD husband, "on the job." She's arranged her widowhood so that she can catch bad guys from a distance, charting the terrible labors of Chris Hansen's likely targets and porn traffickers, then sending SWAT teams to bash in their doors and stop the stink.
At the start of Untraceable, Marsh and her best friend and partner in keyboard-copping, Griffin (Colin Hanks), are joking about his efforts to find love online in between directing takedowns. Solicited by the killwithme webmaster, they're troubled by the fact that his first victim is a kitten, then predictably called off the case by their gruff-and-all-business boss, Brooks (Peter Lewis). Marsh, however, knows something else is up, and it's only a matter of time before she's proved right. The killer targets a hockey fan and, after inviting the cybercrime unit as well as the rest of the U.S. population to watch, leaves the body in a place where the local PD might find it (this detail about only Americans having access is ungainly, and leads to a later argument over jurisdiction with the NSA, yet again inept and irresponsible). Thus Marsh is joined in her efforts by Detective Box (Billy Burke), who, it so happens, knew her husband at the academy.
Before you start imagining that Untraceable is going to delve into complex character relationships, however, it resets its sights precisely on the brutality, sadly leaving Lane with little material, though she does work valiantly against the thin script (see especially, her scenes with Hurt and Jardine). Too often, she and everyone else are relegated to reaction shots, serving as mirrors for viewer responses (these tend to fall between "Yuck!" and "Oh my god!"), as the abundance of images are constituted by the horrors contrived by the killer.
His agenda is tiresome, in the sense that it's both old (see: Natural Born Killers, Stranger Days, Michael Powell's Peeping Tom) and poorly stated. Yes, he's mad at the increasing availability of violent and exploitative media imagery and he means to teach consumers that they are culpable. As this more or less mirrors a possible agenda for the film, some complications arise. As the diegetic "reality" presumably raises stakes for diegetic viewers, the lack of such reality for the film's viewers mostly lets them off hooks, moral and political. As Untraceable pretends to admonish its own viewers for watching not only the torture porn of Saw or Eli Roth, but also the YouTubey excesses offered by terrorists (beheadings, suicide bombings, IEDs) as well as the abuses committed and sometimes repressed by the so-called good guys (Abu Ghraib, the destroyed CIA torture videos).
The trouble is, if everyone's responsible, no one needs to own up. And so, as the camera here focuses intently on the counter indicating the millions of users contributing to each on-screen death, the point turns trivial rather than crucial. While a scene that has Annie stepping outside in pursuit of a camera she's seen surveilling her house is certainly creepy (cutting between shots of Annie from the villain's view, Marsh realizing she's in danger, and Annie's own perspective), this also feels like a trick, the old child-in-danger ploy familiar from any number of slasher flicks and Spielberg.
The mastermind's educational strategy can't succeed, because he is, after all, the killer and so can't be right about anything. Even if you take the film's moral lesson at face value, the overkill is discouraging, and not very instructive.