Officials say there is no evidence the information taken from Los Alamos was sold or transferred to anybody else, but there is no way to be sure right now.
As CBS News correspondent Sharyl Attkisson was the first to report, secret documents apparently taken from the lab were found during a last month. The FBI was called in to investigate.
Multiple sources now tell CBS News that the material includes sensitive weapons-design data.
A federal official who has been briefed on the issue said at least three USB thumb-drives were involved. Those small storage drives contained 408 separate classified documents ranging in importance from Secret National Security Information (pertaining to intelligence) to Secret Restricted Data (pertaining to nuclear weapons).
All of the information came from the classified document video media vault inside the Lab. Federal officials also found 228 pages — printed front and back — of classified documents in the drug trailer during their investigation.
Los Alamos claims to have done a careful and comprehensive analysis of the materials that it believes have been compromised as part of this matter, and has determined that "the majority of the material was classified at the lowest levels and was twenty to thirty years old."
"None of the documents in question were classified Top Secret," read a statement released by the lab. "None of the materials included any of the most sensitive nuclear weapons information."
But one federal official recently briefed on the issue says "It's devastating." If a nuclear weapon were stolen, the information "would tell the terrorists everything they need to do to get a weapon to fire."
Sources say she also had something called Sigma-15 clearance allowing her to access to documents explaining how to deactivate locks on a nuclear weapon.
The woman believed to have taken the information — Jessica Quintana, 22, who owned the trailer — worked in three classified vault rooms across Los Alamos:
She also had top secret "Q-clearance" with access to all the U.S. underground nuclear test data. Quintana has not been arrested or charged. Her attorney says she took the material home to work and then forgot about it.
For example, if a terrorist steals an American nuclear weapon, he could not detonate it due to the special access controls. This woman is authorized to read the reports that tell how to get around those safety controls.
Only the FBI will be able to tell for sure what's on the thumb drives, but British security officials are worried that design plans for Trident nuclear weapons are among the stolen documents. They are making inquiries of U.S. officials. Britain used to test its nuclear weapons in the United States, and data on those tests may have been held at Los Alamos.
Los Alamos has a history of high-profile security problems in the past decade, with the most notable the case of nuclear scientist Wen Ho Lee. After years of accusations, Lee pleaded guilty in a plea bargain to one count of mishandling nuclear secrets at the lab.
In 2004, the lab was essentially shut down after an inventory showed that two computer disks containing nuclear secrets were missing. A year later the lab concluded that it was just a mistake and .
But the incident highlighted sloppy inventory control and security failures at the nuclear weapons lab. The Energy Department then began moving toward a five-year program to create a so-called diskless environment at Los Alamos to prevent any classified material being carried outside the lab.
"We are currently taking decisive actions to further enhance our existing security measures that protect classified information employing both administrative and engineering controls," the lab said in a statement.