The biggest of the cryptocurrencies yet again causing a stir.
Bitcoin hovered above $7,000 on Monday morning, close to nine-month highs.
The volatile currency's reputation meant analysts weren't entirely sure what was behind the surge.
Some said breaking through a key $6,000 support level last week had fuelled interest among investors.
Bitcoin was last up over 1% on the Bitstamp exchange after soaring 14% on Saturday - its second largest daily jump this year.
Analysts and traders said that outsized move did not appear to be the result of any immediate news factors.
Others say bitcoin's resilience in the wake of last week's $40 million theft from the major Binance exchange
was supporting sentiment.
Cryptocurrency markets have previously fallen after high-profile security breaches.
Bitcoin has almost doubled in price this year, after a bruising 2018.
Last year it lost around three-quarters of its value amid tighter regulation around the world.