It's unclear who might be responsible and what the motive may be. This latest attack appears to be more of a nuisance than anything else, but it is raising some concerns.
The White House, State Department, and Federal Trade Commission are just some of the government entities whose websites were knocked off-line for hours.
However, this latest cyber attack targeted companies too, including Yahoo and the Washington Post. Security experts say it was the result of a botnet made up of about 50,000 computers.
"This attack happened because users maybe didn't have maybe didn't have security software installed in their machine, they saw an incoming software attachment, they double-clicked on it, and the next thing you know, their machine is now owned as part of a robotic network or a bot network," says Jerry Egan from Symantec.
That network allows a remote malware author to take control of the infected computers and wreak havoc.
In this latest case, the attack targeted websites in South Korea as well. Lawmakers who were briefed by the /*U.S. Department of Homeland Security*/ say there's no reason to panic. "These cyber attacks did not compromise the functioning of the departments or the ability to communicate with each other," says Democratic Senator Joe Lieberman of Connecticut.
Nor was any information compromised. Still, technology experts say there's reason to be concerned.
"It's just kind of embarrassing," says Bob McMillan.
McMillan is a reporter for IDG News Service -- a technology news wire. He broke the story of this latest cyber attack which he says appears to have been orchestrated by programmers who weren't particularly skilled.
"If this could happen to us, what could happen from a more sophisticated attacker? If we're not ready for the real basic stuff, are we ready for really smart attacks," says McMillan.
According to an anonymous source, South Korea's spy agency told a group of South Korean lawmakers, it believes North Korea was behind the attacks, but that information hasn't yet been confirmed.