On November 6, 2007, Zuckerberg announced Beacon, a social advertising system that enabled people to share information with their Facebook friends based on their browsing activities on other sites. For example, eBay sellers could let friends know automatically what they have for sale via the Facebook news feed as they listed items for sale. The program came under scrutiny because of privacy concerns from groups and individual users. Zuckerberg and Facebook failed to respond to the concerns quickly, and on December 5, 2007, Zuckerberg wrote a blog post on Facebook, taking responsibility for the concerns about Beacon and offering an easier way for users to opt out of the service.