Several officials at the company that manages security at the Los Alamos National Laboratory (LANL) used unprotected email networks to share highly classified data on the characteristics of materials used in nuclear weapons.

The incident occurred on Jan 19 and was considered so serious that a U.S. Department of Energy official was notified of it in the midst of a White House event.

Now, Rep. John Dingell (D-Mich.), chairman of the House Committee on Energy and Commerce, wants to know why a subcommittee investigating an October 2006 security breach at LANL was not told about the January compromise.

Dingell last week wrote a letter to U.S. Department of Energy Secretary Samuel Bodman expressing concern over the failure of the National Nuclear Security Administration to notify the subcommittee of the breach. The NNSA is a semiautonomous body within the DOE that's responsible for supervising the country's nuclear facilities.

In his letter, Dingell noted that NNSA officials learned of the Impact Measurement Index-1 (IMI-1) security incident from an official at a California university on Jan. 19. According to DOE severity ratings, an IMI-1 security incident is the most serious type and is defined as "actions, inactions, or events that pose the most serious threats to national security interests and/or critical DOE assets." Such incidents involve the "confirmed or suspected loss or diversion of a nuclear devices or components or weapons data" and break-ins into systems containing top-secret data, according to a DOE description.

When NNSA learned of the incident, it immediately started working through the Lawrence Livermore National Laboratory to "identify, recover and sanitize" all systems involved, Dingell's letter said. Los Alamos National Security LLC, the contractor responsible for managing security at LANL, initiated an investigation into the event and had completed it by May 18, Dingell said.

"We find it unacceptable that throughout this period, several NNSA, Department of Energy and LANL officials with specific knowledge of this incident met with us on multiple occasions, and a senior LANL official testified twice before the Subcommittee, without mentioning a word about this matter," Dingell said. Instead, all of the information the subcommittee had was provided to its staff by "sources outside of NNSA," he said.

In his letter, Dingell demanded that an unabridged copy of the investigation report and damage assessment be provided to the committee. He also asked for an explanation of why NNSA did not notify the committee of the breach and provide a description of "accountability measures" taken or planned as a result of the breach.