New York: Frauds such as online ponzi schemes have skimmed at least $11 million in Bitcoin deposits from unsuspecting cyber customers over the past four years, a study says.

Bitcoin is the digital world`s most popular virtual currency, with millions in circulation.

"Our calculation of $11 million is almost certainly at the low-end," said lead researcher Marie Vasek from Southern Methodist University in the US.

"The amount of Bitcoin that depositors have lost to these scams is probably many millions more," Vasek added.

The researchers identified 41 scams occurring between 2011 and 2014, in which fraudulent sites stole Bitcoin from at least 13,000 victims.

"We found that the most successful scams draw the vast majority of their revenue from a few victims," Vasek said.

The researchers were only able to track revenues for about 21 percent of the scams, which would indicate that the amount of Bitcoin actually stolen most likely far exceeds $11 million.

There are 13.7 million Bitcoin in circulation, according to blockchain.info. The number of Bitcoin transactions exceeds 100,000 per day.

The researchers identified four common scams by tracking forum discussions, where scams are often initially advertised and later exposed, and by tracking web sites.

Of all the scams, high-yield investment programmes, otherwise known as online Ponzi schemes, which promise investors outlandish interest rates on deposits, have taken in the lion`s share of money from victims, the study noted.

The other three scams identified by the researchers are - mining investment scams, scam wallets and exchange scams.

The findings were presented at the 2015 19th International Financial Cryptography and Data Security Conference in San Juan, Puerto Rico.