It's a stunt which could have come straight from a movie script: an anonymous millionaire leaving cash in envelopes and using social media to help people find their personal pot of gold.
For the past week a mysterious benefactor - identified only as a millionaire real estate developer - has been leaving cash in envelopes in San Francisco and Los Angeles and then publishing clues to their whereabouts on social media.
His only condition: that recipients pay it forward by giving away some of the cash themselves, and reply on social media with a photo proving they have found the cash.
The unnamed philanthropist has been using the Twitter account @HiddenCash, which identifies itself as "an anonymous social experiment for good." It now has more than 270,000 followers.
The envelopes which have been dropped in San Francisco and Los Angeles have contained between US$100 and US$250 in cash.
Despite a sceptical reception from some quarters, he says it is not connected to a viral marketing campaign of any kind.
"Why is it so hard for some to believe that genuine acts of generosity are possible with no ulterior motive? Are we so jaded?" he wrote on Twitter.
The mysterious benefactor has given several interviews to US media but kept his face hidden.
"I’m in that one per cent that some people loathe," he said in one interview. "But rather than hating people who are successful, my point would be to encourage people who have been successful to give back a little bit more."
A Los Angeles television crew from the city's CBS network affiliate, KCBS, filmed him as he planted envelopes in the Los Feliz neighbourhood this week.
"Initially this was just a small, local San Francisco story and it's just gone global," he said, speaking from out of the camera frame. "I want to do some drops here and get the city excited about finding money and just the idea about giving back."
Earlier, he spoke to People magazine saying that he was willing to invest "hundreds of thousands of dollars" in the campaign.
"There is nothing wrong with donating money to a traditional charity, but I also wanted to donate in a more spontaneous way," he said. "This is intended to put a smile on people's faces. I can show people that they can pay it forward."
After San Francisco and Los Angeles, he will shift his focus to New York.
"I want this to expand to other cities," he said. "I want this to become a movement."
- Sydney Morning Herald