Bitcoin tumbled some 12% to trade at $4,980 on CoinDesk.com shortly after 4 p.m. ET Monday, hitting its lowest level in over a year. 

The cryptocurrency has dropped some 20% over the past seven days and has declined more than 60% since 2018 began. Bitcoin futures also hit their lowest levels since their introduction in December 2017, with Bitcoin CME November futures down to $4,855 and Bitcoin contracts on the CBOE down at $4,878.10.

Two factors contributing to the selloff are a split in the cryptocurrency Bitcoin Cash -- which split into two versions last week -- as well as stop-loss orders that kicked in at the $6,000 mark. Increased speculation that increased regulatory scrutiny will prompt issuers of initial coin offerings to liquidate holdings also pushed Bitcoin and other cryptocurrencies lower.

The selloff comes after Bitcoin had been experiencing a level of stability it hasn't seen in some time, holding near the $6,400 mark throughout October before prices started to dip again in early November. The currency's latest declines are the longest string of losses on record for the digital token.
 
Other major cryptocurrencies were down as well on Monday, with Ethereum and Litecoin both down some 14%, according to CoinDesk. Similarly, Ripple was listed nearly 4% lower at 49.4 cents at CoinMarketCap.com, though XRP, the token associated with Ripple, posted gains on the day.

 All told, the combined cryptocurrency market cap sits at around $17 billion, according to CoinMarketCap.com. That's some $15 billion lower than last Friday's levels.

(This article has been updated with afternoon prices.)

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