The Government Accounting Office (GAO), the investigative arm of Congress, blamed the failure of the INS to maintain an integrated, updated database system.
The INS has been unable to locate 45%, of the 4,112 foreigners that the FBI and the government's Foreign Terrorist Tracking Task Force want to interview. The INS has also lost track of 4,334 aliens from countries where al-Qaeda is known to operate who have been ordered to leave the US.
The INS's inability to keep track of the current locations and various address changes of non-immigrants stems from the agency's use of more than 16 database systems to capture the data.
"INS does not update all databases that contain address information and does not have the ability to update address information in Nonimmigrant Information System (NIIS)," said the GAO report.
The NIIS is an automated database that contains address and identity information on non-immigrants who were inspected upon their entry into the US. The GAO also found problems with INS databases in distinguishing among foreigners with the same names.
Robert Diegelman, acting assistant attorney general for administration at the Justice department, under which the INS operates, said the INS has established an address task force to study ways to improve the system, including the creation of a centralised and searchable address repository.
Sanjay Poonen, vice-president of marketing and a homeland security analyst at Informatica, a data integration and business intelligence software developer, said the problems at the INS are indicative of a much larger challenge facing government.
"It's not just about tracking a person as he or she comes into the country; it's also about being able to track that person throughout state and local governments and even into the private sector," said Poonen
The INS estimates that there are 500 million entries into the US each year. Due to the sheer volume of entries and exits and the size of the system that would be required to efficiently handle that volume, the problems highlighted by last year's terror attacks could take a decade to solve, said chief operating officer of security firm Daon, Oliver Tattan said.