The cyber attack on the Department of Defense that has led to a ban on the use of external hardware devices could have come from a number of foreign countries, possibly Russia, though the military is dismissing earlier reports that China was the source of the threat.
FOX News learned that a Navy rear admiral outside the Pentagon, in a briefing to his staff on Thursday, characterized the virus as a coordinated attack that was strategically timed to hit between the Nov. 4 presidential election and Inauguration Day, Jan. 20.
He described how a service member with access to classified information inadvertently loaded the virus onto his computer via a flash drive. As a result, he no longer knows where the computer's sensitive information is being stored.
The cyber attack so alarmed the Pentagon that it took the unprecedented step of banning the use of external hardware devices, such as flash drives and recordable CDs and DVDs.
The attack came in the form of a global virus or worm that is spreading rapidly throughout a number of military networks.
"We have detected a global virus for which there has been alerts, and we have seen some of this on our networks," a Pentagon official told FOX News. "We are now taking steps to mitigate the virus."
The official could not reveal the source of the attack because that information remains classified.
"Daily there are millions of scans of the GIG (the Global Information Grid), but for security reasons we don't discuss the number of actual intrusions or attempts, or discuss specific measures commanders in the field may be taking to protect and defend our networks," the Defense Department said in an official statement.
Military computers are often referred to as part of the GIG, a system of 17 million computers, many of which house classified or sensitive information.
FOX News obtained a copy of a memo sent out last week to an Army division warning of the cyber attack:
"Due to the presence of commercial malware, CDR USSTRATCOM has banned the use of removable media (thumb drives, CDRs/DVDRs, floppy disks) on all DoD networks and computers effective immediately."
FOX News' Justin Fishel and Jennifer Griffin contributed to this report.