A report by the General Accounting Office (GAO) found that $1.2bn (£748m) of security spend was attributable to organisations being folded into the US Department of Homeland Security. The GAO found that this year the figure would rise to $1.3bn.
The GAO reviewed the budgets for 24 government departments and agencies to identify IT projects related to domestic security.
IT infrastructure projects involving multiple agencies, new intelligence systems and funding related to operations at agencies such as Defence and the Federal Aviation Administration put the real IT cost for domestic security much higher than the report indicated.
While the GAO agreed information technology would play an important role in preventing future attacks and improving the nation's domestic security, the report warned that the effectiveness of the federal government's IT investments on security could be undercut by unresolved IT management issues.
The GAO recommended the development of procedures to better secure information, creating an enterprise architecture and managing IT investment and acquisitions.
Most of the agencies reviewed showed significant weaknesses in areas such as programme management, access management and segregation of duties.