The federal government's multibillion-dollar plan to build a virtual fence along the southwestern border was officially canceled Friday, when the Department of Homeland Security said it was shutting down the Secure Border Initiative network.

Homeland Security Secretary Janet Napolitano said the decision, divulged in a congressional briefing, was based on findings that the program known as SBInet was costing too much and achieving too little.

"SBInet cannot meet its original objective of providing a single, integrated border-security technology solution," she said, adding that the department will devise a new security-technology program for the border.

SBInet was conceived in 2005 as a high-tech way to deter, detect and apprehend illegal border-crossers using a surveillance network of ground sensors, video cameras, communication towers and computer software. But it had been troubled almost from the beginning.

Aerospace giant Boeing Corp., a leader in military-defense technology, was hired in 2006 to develop the system under a three-year federal contract. Cost projections for full build-out were as high as $8 billion. Efforts were plagued by delays, glitches, budget increases and congressional criticism. Last year, Napolitano froze some funding and ordered a thorough evaluation of two Arizona pilot projects near Ajo and Tucson.

Analysts found that SBInet helped decrease the flow of illegal immigrants.

But they concluded it was "not the most efficient, effective and economical way to meet our nation's border-security needs."

Napolitano ordered Customs and Border Protection to launch a new effort using SBInet funds and existing technology such as mobile-surveillance systems, unmanned aircraft, thermal-imaging devices and remote-video surveillance. Proven elements of SBInet, stationary radar and infrared-sensor towers, also will be employed.

"This new strategy is tailored to the unique needs of each border region, providing faster deployment of technology, better coverage and a more effective balance between cost and capability," she said.

SBInet cost nearly $1 billion for development along 53 miles of Arizona border. Homeland Security says its new plan can enhance security along the remaining 323 miles of Arizona border at a total cost of less than $750 million.

"I am pleased to hear that Secretary Napolitano finally allowed the SBInet contract to expire," said Sen. John McCain, R-Ariz. "A complete and thorough investigation should be conducted related to this waste."

In a statement, Boeing emphasized that the DHS will continue using some technology developed for SBInet. "We are proud of the accomplishments of our team and of the unprecedented capabilities delivered in the last year that provide Border Patrol agents increased safety, situational awareness and operational efficiency."

While announcing the close of SBInet, Napolitano repeated assertions that security has increased under the Obama administration.

The number of Border Patrol agents more than doubled to 20,500 last year from 10,000 in 2006.