A cryptocurrency that has been derived from the Bitcoin protocol. Since the Bitcoin software was released to the public, hundreds of alternative cryptocurrencies have been published by other people. The Bitcoin source code is available to the public and coders can trivially tweak protocol parameters and create a new altcoin. But there is no guarantee that the public will use and mine the new cryptocurrency, which would increate the security of its ledger. Brand new altcoins often experience 51% attacks from entities (with a large amount of processing power) seeking to disrupt the altcoin and destroy any potential value it may have.

Some popular altcoins include Litecoin, Dogecoin, and Peercoin. A large list of altcoins can be viewed on the wiki.