Facebook has grabbed Hot Potato, a young Internet firm that lets people use smartphones

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to let friends know what they are up to at any given moment.

Hot Potato informed fans of the takeover; just two days after Facebook threw the switch on a new feature that lets US members of the social networking service share their whereabouts with friends while on the move.

"We're excited to confirm that we recently acquired Hot Potato, a service that helps people socialise around live events and share what they're doing with friends," Facebook said in an email response to an AFP inquiry.

"We've admired for some time how Hot Potato is tackling this space and look forward to working with them to bring Hot Potato innovations to Facebook."

Hot Potato about eight months ago launched a social networking service that lets users "check-in" to let friends know what they are thinking, watching, playing, attending, listening to, or otherwise doing.

Hot Potato's approach distinguished it from the growing field of location-based social networks such as Foursquare and Gowalla that let people check into places such as a specific restaurant, park, or theatre.

Whereas Foursquare might let people know a friend checked-in to a local pub, Hot Potato prompts users to complete thoughts including "I'm listening to" and "I'm thinking."

The Hot Potato approach is reminiscent of a private-circle version of Twitter, the hot microblogging service that lets people share thoughts and moments at any time in the form of terse text messages.