Washington (CNN) -- Imagine a battle for U.S. security that never stops. Its skirmishes are fought in milliseconds and its attackers often remain invisible and unknown.
That's the national security battlefield lawmakers want to explore Thursday, in a House Armed Services Committee hearing. Army Gen. Keith Alexander will be the star witness as the person in charge of U.S. Cyber Command.
Alexander -- who also serves as director of the National Security Agency -- was confirmed in May as the first cyber commander. His team of some 1,100 computer experts and military personnel is expected to be fully operating by next month.
The immediacy of the threat to national security was hammered home in August when the deputy defense secretary revealed how crippling a 2008 compromise of the Department of Defense computer system was. An infected flash drive was inserted into a U.S. military laptop in the Middle East and it spread computer code that could transfer U.S. secrets to computers outside the country.
The exact damage has never been revealed. But U.S. Deputy Secretary of Defense William Lynn III, in a recent article in Foreign Affairs magazine, calls it "the most significant breach of U.S. military computers ever, and it served as an important wake-up call." The Pentagon fought back with a program dubbed Operation Buckshot Yankee to root out the rogue program and, where possible, to limit the damage.
In that same article, Lynn says that military and civilian computer networks are probed thousands of times and scanned millions of times each day.
"The 2008 intrusion that led to Operation Buckshot Yankee was not the only successful penetration. Adversaries have acquired thousands of files from U.S. networks and from the networks of U.S. allies and industry partners, including weapons blueprints, operational plans, and surveillance data."
"Cyber attacks pose one of the greatest threats to our national security, and it's important for our committee to closely watch this to make sure we get it right," said House Armed Services Committee Chairman Ike Skelton.
Alexander will appear before the full Armed Services Committee in the morning and then representatives of the Army, Navy, Air Force and Marines will appear before a subcommittee Thursday afternoon to tell how the individual services are coping with cyber threats.