The bitcoin system was under threat recently when some miners were reluctant to upgrade their systems to improve capacity because it could reduce transaction fees they collect. Refusal would have sowed chaos, as no one could be sure which bitcoin belonged to the old or new system. But miners ended up agreeing to the change by the deadline.
Still, a group of developers created an alternate currency, Bitcoin Cash, last week. So far, many individuals, businesses and criminal enterprises consider bitcoin the digital currency of choice, but that could change if any of the alternatives pick up steam.