People with metal detectors dug through the sand of a US beach after an anonymous man with the Twitter handle HiddenCash tweeted about the location of a posh scavenger hunt.

The anonymous benefactor buried 36 small plastic Angry Birds orbs stuffed with cash in southern California. The account then tweeted: "Hermosa Beach, between the pier and the volleyball nets to your left (as you face the ocean)," at about 11.30am. "Go!" Most were found by 5pm.

The same Twitter persona directed people to envelopes with 50 dollar and 100 dollar bills inside them in San Francisco. The cash-dropper says his giveaways are a "social experiment for good".

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