Irrespective of pump and dump as described above, cryptocurrencies often have small volumes, often a few hundred or thousand dollars a day. So its very easy for someone to come in and start a rally by buying up the market, especially if only one or two exchanges trade it. The speculators latch onto it and before you know it the crypto increased several hundred percent. If you hear about the crypto after its big boost, steer clear. Look for cryptos that have a solid core community and do something truly unique.