clipped from blog.wired.com

Researchers Use Facebook App to Create Zombie Army – Update

Computer researchers built a tool that demonstrates how hackers could silently turn Facebook users into a powerful zombie army that can attack other websites or scout for vulnerable sites on the net.

Their demo attack was very simple and surprisingly effective. They created an application that displayed a new National Geographic photo daily on a user’s Facebook page — though the app was not approved of by National Geographic.

But in the background, the application is also downloading three large photos from a targeted site. But the user’s browser never displays the images. Any application with enough users will then act like a denial of service attack flooding the chosen website with requests for data. The user stops being a part of the attack after logging out, but joins again every time he returns.