- Coinrail, a relatively small South Korean cryptocurrency exchange, tweeted over the weekend that it was hacked, according to Google Translate.
- Bitcoin fell more than 10 percent to a low of $6,647.33, its lowest since April 9, according to CoinDesk's bitcoin price index.
- The decline followed a report on Friday from The Wall Street Journal that U.S. regulators are investigating potential price manipulation at four major cryptocurrency exchanges.
Bitcoin tumbled more than 10 percent over the weekend to its lowest in two months, after a relatively small South Korean exchange said it was hacked.
Over the weekend, crypto exchange Coinrail tweeted that it was hacked, and noted that lesser-known cryptocurrencies such as Pundi X were among those affected, according to Google Translate. The Pundi X-bitcoin pair is the most-traded on Coinrail, CoinMarketCap data showed.
However, Coinrail's public statements did not mention bitcoin, according to Google Translate.
Nevertheless, Bitcoin hit a low of $6,647.33 on Sunday, its lowest since April 9, according to CoinDesk's bitcoin price index, and coincided with a broader crypto sell-off. The digital currency traded off those lows Monday afternoon, near $6,700.
The largest cryptocurrency by market capitalization remains about 50 percent lower for the year so far.
Bitcoin three-month performance
Other major cryptocurrencies also fell. Ethereum dropped more than 11 percent to near $533, according to CoinDesk.
The declines followed a report on Friday from The Wall Street Journal, citing sources, that U.S. regulators are investigating potential price manipulation at four major cryptocurrency exchanges: Bitstamp, Coinbase, itBit and Kraken.
"We support all market participants, exchanges, regulators in having a dialogue to enhance transparency and find common ground," Chad Cascarilla, CEO and co-founder of Paxos, which owns cryptocurrency exchange itBit, said in a statement. The three other cryptocurrency companies did not immediately respond to a CNBC request for comment on Sunday evening.
CME said exchanges contributing to its Bitcoin Reference Rate — which include the four above — are required to share information and cooperate with regulators. The Commodity Futures Trading Commission would not confirm or deny any investigative activity.