Tyler and Cameron Winklevoss have put $1 million into SumZero, which was founded by fellow Harvard University alumni Divya Narendra and Aalap Mahadevia in 2008, the article said. Narendra was an ally to the Winklevoss twins during their lawsuit against Facebook, which won the brothers a cash and stock settlement valued at $65 million at a time when the company was valued at $15 billion.

Facebook's market cap is currently valued at $47 billion.

In June 2011, the twins decided not to appeal to the U.S. Supreme Court a ruling upholding their $65 million settlement.

The 2008 accord was intended to resolve a feud over whether Zuckerberg stole the idea for what became the world's most popular social networking website from the Winklevosses, who like him, had attended Harvard. Their battle was dramatized in the 2010 film "The Social Network."

After agreeing to the cash-and-stock accord, the Winklevosses sought to undo it, saying it was fraudulent because Facebook hid information from them and that they deserved more money.

In February, the brothers formed Winklevoss Capital as a vehicle to invest their personal wealth. Their first investment in June was SumZero, which brings together investors to share trading ideas and research, the WSJ reported.

SumZero.com has 7,500 members and has parallels with the first versions of Facebook, including exclusivity.

The site also allows investors to become members only if they work on the "buy side." SumZero defines that group as investment professionals at hedge funds, mutual funds and private-equity firms. Analysts from the "sell side" such as Wall Street banks are not allowed, the report said.

(Reporting by Nadia Damouni, editing by Gary Crosse)

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