The issue is a new feature called Facebook Beacon, launched in New York earlier this month as part of Facebook Ads. Designed to attract advertisers, the Beacon shines light on the purchases members make when they are not even on the Facebook site…

For example, in the case of Helfgott’s girlfriend, she was shopping on Overstock.com, one of Facebook’s new partners. She did not visit Overstock.com from Facebook’s Web site, and apparently did not see the messages telling her that her purchases would be sent to her news feed on Facebook unless she clicked no.

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Facebook may become the Grinch who stole Christmas - MarketWatch

I think a lot of this data privacy stuff is overblown.  But this is pretty crazy.  Have to believe Facebook will modify this, a la how they modified the News Feed when it originally came out.