Bitcoin exchanges are again making headlines and not for the reasons they'd like. U.S. authorities are launching an investigation into whether Bitcoin exchanges and other related businesses have any tangible ties with the dark web drug bazaar Silk Road.

Those familiar with the matter recently told the Wall Street Journal that the investigation is at an early stage. We are told that embattled Bitcoin exchange Mt. Gox was among those that received a subpoena from Manhattan federal prosecutors during the winter.

According to sources, prosecutors and FBI agents demanded to see customer transaction logs as well as material related to solicitation of investors. What's more, they're also looking into whether the exchange and others processed transactions connected to Silk Road.

It's unclear which other Bitcoin-related businesses might be under the microscope.

Earlier this year, BitInstant co-founder and CEO Charlie Shrem was arrested and charged with money laundering. Much like Mt. Gox, his company would swap fiat currency for virtual currency and vice verse, collecting a fee on each transaction.

But it's Mt. Gox that has been stealing Bitcoin-related headlines this year. The exchange shut down without warning on February 25, filing for bankruptcy a few days later. Mt. Gox claimed hackers stole some 850,000 Bitcoins (around seven percent of the total Bitcoins in circulation) worth more than $500 million at the time. They later claim to have found 200,000 Bitcoins stored in an old-format virtual wallet.