INTERNET - Latest target of MoveOn: Facebook - The advocacy group says the site's ad system violates users' privacy.

At issue is Facebook's new advertising program that lets its members notify friends about movies they rent, items they auction and movie tickets they buy at partner sites elsewhere on the Web.

Facebook allows its members to opt out of the ad system, called Beacon. But MoveOn.org contends the program violates users' privacy by requiring them to opt out rather than voluntarily opt in. "The sole reason for this new feature is to serve corporate advertisers and make it easier for them to micro-target Facebook users with ads," MoveOn .org spokesman Adam Green said. "Breaching privacy is against the type of community Facebook should be striving for."

MoveOn.org is buying ads, organizing a "protest group" and circulating an online petition to pressure Facebook to allow its more than 55 million users to change its opt-out method.

By early Tuesday evening, the protest group numbered 2,568 with several members threatening to quit Facebook. They complained that holiday gift surprises had been spoiled. Matthew Helfgott, a 20-year-old college student from Long Island, said he spotted his girlfriend's Hanukkah gift to him of a pair of gloves.

"I sure as hell wouldn't be opting in on everything," said Tasha Valdez, 27, who lives in a Detroit suburb. "If I wanted to tell my friends about something like that, I would post it myself."

Others are concerned that more sensitive activities and purchases could bring unwanted and potentially harmful attention to users.

Facebook spokeswoman Brandee Barker said MoveOn .org was playing politics.

"Beacon gives users an easy way to share relevant information from other sites with their friends on Facebook," she said. "Users also are given multiple ways to choose not to share information from a participating site, both on that site and on Facebook."

Facebook says it works like this: When a user buys a movie ticket, a pop-up box tells the user it's sending that information to Facebook. The user can click "No thanks." If the user doesn't, the next time he or she visits Facebook, a message will pop up asking for permission to share that data with his or her friends.