In a bit of unfortunate timing, the C.I.A.'s website was shut down for a couple of hours yesterday evening in an apparent cyber attack. It was only a week ago that Leon Panetta, the C.I.A.'s outgoing director, warned senators that cyber warfare could be the next big battleground for the United States.

"The next Pearl Harbor we confront could very well be a cyber attack that cripples our power systems, our grid, our security systems, our financial systems, our governmental systems," he told the Senate Armed Services Committee during his confirmation hearing to replace Bob Gates as secretary of defense.

Yesterday's attack on the C.I.A. was in the form of a denial of service, meaning the hackers flooded the site with requests for access, effectively shutting down the server. While it certainly doesn't rise to the level of causing crippling damage, it is an embarrassment for the agency and highlights just how vulnerable our cyber infrastructure is.

The hacker group claiming responsibility for the attack calls itself LulzSec and describes itself as "the world's leaders in high-quality entertainment at your expense." They claimed credit via twitter yesterday with the message: "Tango down - cia.gov-for the lulz."

The group has also claimed responsibility for a string of other high profile attacks in recent weeks on the U.S. Senate, Sony, and PBS.

A U.S. official said it was important to keep in mind the site wasn't technically "hacked" since the attackers weren't able to get into the system, but acknowledged the two-hour episode was "annoying."

"These kind of issues can affect any website," the official said. "In this case it was resolved quickly."