MUMBAI: Despite the Reserve Bank's call for caution to people against the use of virtual currencies, a domestic Bitcoin exchange today said it is adding over 2,500 users a day and has reached five lakh downloads.Zebpay, an app-absed Bitcoin exchange, said it has had five lakh downloads on the Android operating system and is adding more than 2,500 users every day.The company, launched in 2015, said, the increasing downloads highlight the "growing acceptance of Bitcoins as one of the most popular emerging asset class."RBI has been repeatedly flagging concerns on virtual currencies like Bitcoins, stating that they pose potential financial, legal, customer protection and security-related risks.In recent cyber attacks, " ransomware '' hackers held victims hostage by encrypting their data and demanding them to send payments in bitcoins to regain access to their computers.Bitcoin is a digital currency that allows people to buy goods and services and exchange money without involving banks, credit card issuers or other third parties.Bitcoin is not tied to a bank or government and allows users to spend money anonymously. The coins are created by users who 'mine' them by lending computing power to verify other users' transactions.They receive bitcoins in exchange. The coins also can be bought and sold on exchanges with US dollars and other currencies.One bitcoin recently traded for $1,734.65, according to Coinbase, a company that helps users exchange bitcoins. That makes it more valuable than an ounce of gold, which trades at less than $1,230.The value of bitcoins can swing sharply, though. A year ago, one was worth $457.04, which means that it's nearly quadrupled in the last 12 months. But its price doesn't always go up.A bitcoin's value plunged by 23 per cent against the dollar in just a week in January. It fell by the same amount again in 10 days during March.Bitcoins are basically lines of computer code that are digitally signed each time they travel from one owner to the next. Transactions can be made anonymously, making the currency popular with libertarians as well as tech enthusiasts, speculators and criminals.Yes, to a point. Transactions and accounts can be traced, but the account owners aren't necessarily known. However, investigators might be able to track down the owners when bitcoins are converted to regular currency.For now, the three accounts tied to the ransomware attack appear untouched -- and it'll be difficult for perpetrators to cash in anytime soon without getting traced.Some businesses have jumped on the bitcoin bandwagon amid a flurry of media coverage. Overstock.com accepts payments in bitcoin, for example. The currency has become popular enough that more than 300,000 daily transactions have been occurring recently, according to bitcoin wallet site blockchain.info. A year ago, activity was closer to 230,000 transactions per day.The bitcoin network works by harnessing individuals' greed for the collective good. A network of tech-savvy users called miners keep the system honest by pouring their computing power into a blockchain, a global running tally of every bitcoin transaction.The blockchain prevents rogues from spending the same bitcoin twice, and the miners are rewarded for their efforts by being gifted with the occasional bitcoin. As long as miners keep the blockchain secure, counterfeiting shouldn't be an issue.It's a mystery. Bitcoin was launched in 2009 by a person or group of people operating under the name Satoshi Nakamoto. Bitcoin was then adopted by a small clutch of enthusiasts. Nakamoto dropped off the map as bitcoin began to attract widespread attention. But proponents say that doesn't matter: The currency obeys its own internal logic.An Australian entrepreneur last year stepped forward and claimed to be the founder of bitcoin, only to say days later that he did not 'have the courage' to publish proof that he is.