E-gold

E-gold was an early attempt to create digital currency. Unlike later systems such as Bitcoin, E-gold operated through a central service which tracked account balances and physically held the gold with which the currency was backed, which made it a target when the government decided to go after them for money laundering (a double-cross by the government given that the operators of E-gold had earlier specifically approached the government to find out what legal category their business fell into and whether any licencing or regulation applied to it, and was told that they weren't a regulated cash-transfer service because they dealt in gold instead of currency). The prosecution put the service out of business, and later digital currencies generally took as the lesson from this that they needed to be completely decentralized, as well as not actually backed by anything physical such as gold, in order to keep from having anything the government could shut down or seize that would put a complete stop to the currency.

Links

 * Wikipedia article
 * Official site, or what's left of it