Someone is dropping envelopes full of cash across San Francisco - and causing an international frenzy on social media.
An anonymous man with the Twitter handle @HiddenCash has been hiding money throughout the city since last Friday, leading scores on a scavenger hunt. His Twitter following is now at more than 80,000.
One of his clues on Tuesday told followers to "find Mr. Franklin along the 'crookedest street,' (towards the bottom)".
Translation: There was a US$100 bill at the bottom of Lombard Street, a popular tourist thoroughfare that is known as the most crooked street in the world.
Hidden Cash's anonymous creator said his giveaways were a "social experiment for good".
He claims to make his money off San Francisco's hot and lucrative real-estate market and hopes that winners also "pay it forward".
Two of his winners said that they did just that.
Sergio Loza, 28, of San Francisco, said he saw a clue on Twitter with the message: "Early bird gets the worm."
He raced out and found an envelope with US$50 inside, taped to a parking meter in the city's Mission District.
Loza said he spent US$30 on clothes for his two-year-old niece's birthday and gave her the remaining US$20 as well.
"I didn't spend it on myself," said Loza, a security guard. "It feels good to give, especially in these times."
Adam Wenger, 27, said he won US$200 by finding two envelopes within about two hours in the city's South of Market district. One envelope read: "With Love, from @HiddenCash. Leave $20 somewhere and pay it forward."
Wenger, a web producer for KGO radio, bought pizza for his co-workers and plans to pay a US$100 parking ticket.
"It's crazy," he said.
The anonymous benefactor said on Twitter that he planned to leave envelopes in San Jose on Wednesday, Los Angeles this weekend and maybe New York next month.
Followers have requested similar gestures from as far away as Pakistan.
Loza said he sent @HiddenCash "a big shout-out" on Twitter, thanking him for the money.
"I hope he keeps it up," Loza said. "While you probably can't help the whole world, a few at a time is definitely good."