When a teenage boy snatched the iPhone out of Rose Cha’s hand at a bus stop in the Bronx in March, she reported the theft to her carrier and to the police — just as she had done two other times when she was the victim of cellphone theft. Again, the police said they could not help her.

Ms. Cha’s phone was entered in a new nationwide database for stolen cellphones, which tracks a phone’s unique identifying number to prevent it from being activated, theoretically discouraging thefts. But police officials say the database has not helped stanch the ever-rising numbers of phone thefts, in part because many stolen phones end up overseas, out of the database’s reach, and in part because the identifiers are easily modified.

Little incentive

Some law enforcement authorities, though, say there is a bigger issue — that carriers and handset makers have little incentive to fix the problem.

“The carriers are not innocent in this whole game. They are making profit off this,” said Cathy L. Lanier, chief of the police department of the District of Columbia, where a record 1,829 cellphones were taken in robberies last year.

George Gascón, San Francisco’s district attorney, says handset makers like Apple should be exploring new technologies that could help prevent theft. In March, he said, he met with an Apple executive, Michael Foulkes, who handles its government relations, to discuss how the company could improve its anti-theft technology. But he left the meeting, he said, with no promise that Apple was working to do so.

He added, “Unlike other types of crimes, this is a crime that could be easily fixed with a technological solution.”

Apple declined to comment.

The cellphone market is hugely lucrative, with the sale of handsets bringing in $69 billion in the United States last year, according to IDC, the research firm. Yet, thefts of smartphones keep increasing, and victims keep replacing themIn San Francisco last year, nearly half of all robberies involved a cellphone, up from 36 per cent the year before; in Washington, cellphones were taken in 42 per cent of robberies, a record. In New York, theft of iPhones and iPads last year accounted for 14 per cent of all crimes.

Carriers say they have faith in the database, which they created with police departments across the country. They also say they are taking independent steps as well to address the problem. Apple provides some assistance in locating lost or stolen phones with its free software, Find My iPhone, which can find a missing iPhone or remotely erase its data. But the service does not work once the phone is turned off or disconnected from the Internet. Google does not include any software in its Android operating system to help people locate a missing phone, although some third-party Android apps offer the feature. Mr. Gascón of San Francisco said that was not enough. “What I’m talking about is creating a kill switch so that when the phone gets reported stolen, it can be rendered inoperable in any configuration or carrier,” he said.

Security solutions

Some security experts say such solutions are possible. One is software to prevent a phone from working after it is reported stolen, said Kevin Mahaffey, chief technology officer of Lookout, a mobile security firm. There would be ways to work around that, he said, but if companies made it time-consuming and expensive to reactivate a stolen cellphone, then people would stop stealing them so much.

Often, stolen phones are moved to a house or storage facility where middlemen erase the phone’s memory, Mr. Santos said. Clearing a phone makes it difficult for the police to prove a phone was stolen and to return it to its owner.

Erasing IMEI

In at least one case, Mr. Santos said, people suspected of stealing phones were found to be hacking the phones’ unique identifying code, known as an International Mobile Station Equipment Identity, essentially erasing all digital evidence that the phone was stolen. This also makes it possible to reactivate a stolen phone, even after it has been entered into the database.

Mr. Santos said he suspected that this kind of modification was widespread.

Recent cellphone theft cases in San Francisco suggest that many end up as far away as Mexico, Vietnam and China.

The international reach, huge profits and technological expertise of these black market operators suggest possible ties to larger organised crime networks, Mr. Santos said.

“It could be just a bunch of small groups, but these guys are very well organised, very tech savvy, well trained and well funded,” he said. “I think it is just a matter of time before we find the mother lode, a warehouse that is just stacked to the ceiling with smartphones.” — New York Times News Service