Cryptocurrencies dropped on Thursday as Bitcoin gave up the $4,000 level it\u2019s hovered around since the start of the year. The largest digital currency slumped as much as 6.2% in the European morning, erasing an earlier small gain to trade at $3,785.17 at 9:28 am in London. The Bloomberg Galaxy Crypto Index, a gauge of the largest cryptocurrencies, fell 7.7% as Bitcoin\u2019s rival tokens, including Ether, Litecoin and XRP, also retreated. ALSO READ:\u00a0GST Council meet: Relief for small businesses as exemption limit doubled; key things to know Timothy Tam, co-founder and CEO of CoinFi, a cryptocurrency research firm in Hong Kong, said while there wasn\u2019t an immediate reason for the abrupt sell-off, he did notice a large transfer of about 40,000 Ether into an exchange an hour before the drop. \u201cUsually transfer of Ethereum onto an exchange indicates an intent to sell, and if there is a sell-off on one exchange it compounds like dominoes to another because arbitragers will sell immediately on the other exchanges as well,\u201d he said.