DOD officials told senators they are working to prevent a similar data breach from happening again. The DOD has disabled data transfers to removable media on most computers in combat zones, said Teresa Takai, the DOD's CIO. About 12 percent of computers in combat zones retain the capability to transfer data to removable media, for "operational reasons," she said.

The DOD has put strict controls on the computers that still have removable media capabilities, she added. The DOD is also working with other agencies on an insider threat program, she said.

While senators raised concerns about the breach, they also questioned critics who have called for less information sharing between U.S. defense and intelligence agencies. A lack of information sharing between agencies aided the Sept. 11, 2001, terrorists, said Senator Joe Lieberman, a Connecticut independent.

There are continued problems with agencies not sharing information, he added. Before the November 2009 shootings at Fort Hood, Texas, the U.S. Federal Bureau of Investigation had information about the ties of suspect Nidal Malik Hasan, an Army major, to radical Islam, Lieberman noted.

Lieberman said he fears that agencies may be reluctant to share information after the WikiLeaks scandal. "To me, this is like putting an axe to a problem that requires a scalpel," he said. "We can and must prevent another WikiLeaks without also enabling federal agencies -- in fact, perhaps, compelling federal agencies -- to reverse course and return to the pre-9/11 culture of hoarding information."