The US Department of Defence took an estimated 1,500 computers offline on Wednesday after a security breach within the Office of the Secretary of Defence (OSD).
"Elements of the OSD unclassified email system were taken offline yesterday afternoon, due to a detected penetration," US defence secretary Robert Gates said. "A variety of precautionary measures are being taken. We expect the system to be online again very soon."
Gates said there was "no anticipated adverse impact" on ongoing operations. "There will be some administrative disruptions and personal inconveniences. It will come as no surprise that we aggressively monitor intrusions and have appropriate procedures to address events of this kind. But as I say, we get perhaps hundreds of attacks a day."
The defence secretary said he was not sure why the 1,500 users were removed temporarily from the system. "Well, I don't know the answer to that, and they're still investigating it," he said.
However, it looks as if the defence secretary will not be personally inconvenienced. "I don't do email," he said in response to a question. "I'm a very low-tech person."
The Pentagon security breach follows last month's breach at the US Department of Homeland Security, where a hard drive containing details of 100,000 staff went missing. This week, the department is holding a hearing to discuss the findings of an investigation into the agency's problems in battling electronic attacks and IT systems intrusions.