The value of bitcoin virtual currency was down sharply Tuesday, after a major online exchange for the currency abruptly closed its website.
At the same time, rumors circulating through the Internet suggested that hackers had stolen as much as six percent of all bitcoins from the Mt. Gox exchange.
The Japan-based digital currency operator closed its website Tuesday and its offices did not respond to requests for comment. Later, Mt. Gox posted a brief notice saying it closed all transactions to "protect the site" and its users.
Earlier this month, Mt.Gox halted withdrawals of bitcoins, citing "unusual activity," prompting angry protests from investors.
Internet reports say that hackers have been secretly stealing bitcoins for years and that Mt. Gox lost 744,000 bitcoins out of 12.4 million currently in circulation.
One of the websites that follow the price of bitcoin, Bitwat.ch, places its current value at less than $500, down from above $1,200 in November.
Bitcoin is one of several so-called cryptocurrencies circulating around the world allowing individuals and companies to make digitally coded payments without fees usually charged by financial companies.
Since its introduction in 2009, bitcoin has seen several sharp rises and drops in its value.