WASHINGTON (Reuters) - The "Shamoon" virus that attacked Saudi Arabia's state oil company, ARAMCO, was probably the most destructive attack the business sector has seen to date, U.S. Defense Secretary Leon Panetta said on Thursday.

Addressing business leaders in New York, Panetta described the virus as sophisticated and noted that a similar attack days later struck Qatar's natural gas firm, Rasgas.

"More than 30,000 computers that it infected (at ARAMCO) were rendered useless, and had to be replaced," he said.

He said Shamoon included a routine called a "wiper," coded to self-execute, which replaced crucial system files with an image of a burning U.S. flag. It also overwrote all the real data on the machine with what he called garbage data.

"Imagine the impact an attack like this would have on your company," Panetta said, as he called for steps to bolster the nation's cyber defenses.

In his speech, Panetta also cited recent denial-of-service attacks against major U.S. banks, which delayed or disrupted services on customer websites.

"While this kind of tactic isn't new, the scale and speed with which it happened was unprecedented," he said.

One U.S. official, briefing reporters before the speech on condition of anonymity, said the United States knew who carried out the attacks cited in Panetta's speech, but declined to disclose that information.

(Reporting by Phil Stewart; Editing by Peter Cooney)

Earlier on HuffPost:

Loading Slideshow...
  • #9: Pakistan

    Pakistan relays <strong>3.3 percent</strong> of all spam.

  • #8: Poland

    Poland relays <strong>3.9 percent</strong> of all spam.

  • #7: Brazil

    Brazil relays <strong>4.3 percent</strong> of all spam.

  • #6: Italy

    Italy relays <strong>4.9 percent</strong> of all spam.

  • #4, Tied: Russia

    Russia is tied with Indonesia for fourth place, relaying <strong>5 percent</strong> of all spam.

  • #4, Tied: Indonesia

    Indonesia is tied with Russia for fourth place, relaying <strong>5 percent</strong> of all spam.

  • #3: South Korea

    South Korea relays <strong>5.7 percent</strong> of all spam.

  • #2: United States

    The United States relays <strong>8.3 percent</strong> of all spam.

  • #1: India

    India relays a whopping <strong>9.3 percent</strong> of all spam to computers across the world.

  • ALSO ON THE HUFFINGTON POST

    Spam. Depending on your tastes it's a a) delicious or b) vile canned meat product from Hormel. If you're a computer user there is no a) / b) proposition; spam sucks. Michael "Doctor File Finder" explains what exactly spam is and how to eradicate or, at least, lessen its impact on your inbox. Spam is the plague of the Internet and nearly 90% of all the email that's sent is spam. We'll show you some ways to reduce the amount of spam you have to deal with.