Cryptocurrency prices were sharply lower Monday, with the No. 1 digital currency trading at a weekly nadir as popular sites banned digital-currency advertisement.

A single bitcoin BTCUSD, +0.24% last traded at $7,885.15, down 6.7% on the day, and well off its overnight high of $8,489.61, according to news-and-research site CoinDesk.

The plummet in cryptocurrency prices comes as Twitter Inc. TWTR, +0.20% confirmed last week's rumors that it would join Facebook Inc. FB, +0.04% and Google-parent Alphabet Inc. GOOG, +0.39% GOOGL, +1.99%  in banning advertising of cryptocurrencies and a novel venture raising method known as ICOs, or initial coin offerings.

After staging a relief rally early last week, the price of a single bitcoin is in danger of breaking the Feb 6. low of $5,947.40, which technicians see as a pivotal support level.

Monday's slide comes after a record week of low volatility.

As equity volatility rises, bitcoin's subsides

Despite the surging volatility in the stock market, bitcoin is coming off its quietest week in a long time. Last week's range in the Cboe bitcoin April contract XBTJ8, -0.13% of $8,100 to $9,190 was the tightest since the contract listed in late January, according to the Cboe Options Exchange.